Re: [syzbot] [ext4?] KASAN: use-after-free Read in ext4_ext_insert_extent

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in ext4_find_extent

==================================================================
BUG: KASAN: slab-use-after-free in ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
BUG: KASAN: slab-use-after-free in ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
Read of size 4 at addr ffff88807e32ee18 by task syz.0.121/7280

CPU: 1 UID: 0 PID: 7280 Comm: syz.0.121 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
ext4_ext_map_blocks+0x288/0x6ac0 fs/ext4/extents.c:4214
ext4_map_query_blocks+0x13b/0x930 fs/ext4/inode.c:550
ext4_map_blocks+0x4b3/0x1740 fs/ext4/inode.c:773
_ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943
ext4_block_write_begin+0x990/0x1710 fs/ext4/inode.c:1198
ext4_write_begin+0xc04/0x19a0 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x445/0xda0 fs/ext4/inode.c:3129
generic_perform_write+0x2c2/0x900 mm/filemap.c:4175
ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c6/0xb30 fs/read_write.c:686
ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2f49d8e969
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f2f4ab1e038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f2f49fb5fa0 RCX: 00007f2f49d8e969
RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007f2f49e10ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f2f49fb5fa0 R15: 00007ffdd4fbb178
</TASK>

Allocated by task 6267:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4376 [inline]
__kmalloc_noprof+0x27a/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]
tomoyo_realpath_from_path+0xe3/0x5d0 security/tomoyo/realpath.c:251
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_check_open_permission+0x1c1/0x3b0 security/tomoyo/file.c:771
security_file_open+0xb1/0x270 security/security.c:3144
do_dentry_open+0x384/0x13f0 fs/open.c:942
vfs_open+0x3b/0x340 fs/open.c:1095
do_open fs/namei.c:3975 [inline]
path_openat+0x2ee5/0x3830 fs/namei.c:4134
do_filp_open+0x1fa/0x410 fs/namei.c:4161
do_sys_openat2+0x121/0x1c0 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_openat fs/open.c:1466 [inline]
__se_sys_openat fs/open.c:1461 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1461
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6267:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:243 [inline]
__kasan_slab_free+0x5b/0x80 mm/kasan/common.c:275
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2422 [inline]
slab_free mm/slub.c:4695 [inline]
kfree+0x18e/0x440 mm/slub.c:4894
tomoyo_realpath_from_path+0x598/0x5d0 security/tomoyo/realpath.c:286
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_check_open_permission+0x1c1/0x3b0 security/tomoyo/file.c:771
security_file_open+0xb1/0x270 security/security.c:3144
do_dentry_open+0x384/0x13f0 fs/open.c:942
vfs_open+0x3b/0x340 fs/open.c:1095
do_open fs/namei.c:3975 [inline]
path_openat+0x2ee5/0x3830 fs/namei.c:4134
do_filp_open+0x1fa/0x410 fs/namei.c:4161
do_sys_openat2+0x121/0x1c0 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_openat fs/open.c:1466 [inline]
__se_sys_openat fs/open.c:1461 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1461
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88807e32e000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 3608 bytes inside of
freed 4096-byte region [ffff88807e32e000, ffff88807e32f000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7e328
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a042140 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a042140 0000000000000000 dead000000000001
head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0001f8ca01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5163, tgid 5163 (rcS), ts 23112480838, free_ts 21314138532
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21d5/0x22b0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2660
new_slab mm/slub.c:2714 [inline]
___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
__slab_alloc mm/slub.c:3992 [inline]
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]
__kmalloc_cache_noprof+0x296/0x3d0 mm/slub.c:4402
kmalloc_noprof include/linux/slab.h:905 [inline]
tomoyo_print_header security/tomoyo/audit.c:156 [inline]
tomoyo_init_log+0x183/0x1f70 security/tomoyo/audit.c:255
tomoyo_supervisor+0x340/0x1480 security/tomoyo/common.c:2198
tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
tomoyo_path_permission+0x25a/0x380 security/tomoyo/file.c:587
tomoyo_path_perm+0x392/0x4b0 security/tomoyo/file.c:838
security_inode_getattr+0x12f/0x330 security/security.c:2377
vfs_getattr fs/stat.c:259 [inline]
vfs_statx_path fs/stat.c:299 [inline]
vfs_statx+0x18e/0x550 fs/stat.c:356
vfs_fstatat+0x118/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat fs/stat.c:536 [inline]
__x64_sys_newfstatat+0x116/0x190 fs/stat.c:536
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
page last free pid 1 tgid 1 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbb1/0xd20 mm/page_alloc.c:2895
__free_pages mm/page_alloc.c:5260 [inline]
free_contig_range+0x1bd/0x4a0 mm/page_alloc.c:7091
destroy_args+0x69/0x660 mm/debug_vm_pgtable.c:958
debug_vm_pgtable+0x39f/0x3b0 mm/debug_vm_pgtable.c:1345
do_one_initcall+0x233/0x820 init/main.c:1271
do_initcall_level+0x104/0x190 init/main.c:1333
do_initcalls+0x59/0xa0 init/main.c:1349
kernel_init_freeable+0x334/0x4b0 init/main.c:1581
kernel_init+0x1d/0x1d0 init/main.c:1471
ret_from_fork+0x439/0x7d0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
ffff88807e32ed00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88807e32ed80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807e32ee00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88807e32ee80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88807e32ef00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


Tested on:

commit: 30d4efb2 Merge tag 'for-linus-6.18-rc1-tag' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16a00a7c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7a4d61c2af99e8dd
dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch: https://syzkaller.appspot.com/x/patch.diff?x=119d2334580000

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:

KASAN: use-after-free Read in ext4_ext_correct_indexes

==================================================================
BUG: KASAN: use-after-free in ext4_ext_correct_indexes+0x72/0x5b0 fs/ext4/extents.c:1712
Read of size 8 at addr ffff888078dca350 by task syz.2.45/6689

CPU: 0 UID: 0 PID: 6689 Comm: syz.2.45 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595

ext4_ext_correct_indexes+0x72/0x5b0 fs/ext4/extents.c:1712
ext4_ext_insert_extent+0x1fdd/0x4af0 fs/ext4/extents.c:2188
ext4_ext_map_blocks+0x1bbe/0x3880 fs/ext4/extents.c:4410
ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
ext4_map_blocks+0x860/0x1740 fs/ext4/inode.c:811

_ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943
ext4_block_write_begin+0x990/0x1710 fs/ext4/inode.c:1198
ext4_write_begin+0xc04/0x19a0 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x445/0xda0 fs/ext4/inode.c:3129
generic_perform_write+0x2c2/0x900 mm/filemap.c:4175
ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c6/0xb30 fs/read_write.c:686
ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f9e7b78e969

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f9e7a9fe038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f9e7b9b5fa0 RCX: 00007f9e7b78e969

RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004

RBP: 00007f9e7b810ab1 R08: 0000000000000000 R09: 0000000000000000

R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 00007f9e7b9b5fa0 R15: 00007fff3dade2a8
</TASK>

The buggy address belongs to the physical page:

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888078dcadc0 pfn:0x78dca
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea00016119c8 ffffea00018708c8 0000000000000000
raw: ffff888078dcadc0 ffff888079136c60 00000000ffffffff 0000000000000000

page dumped because: kasan: bad access detected

page_owner tracks the page as freed
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x440dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_COMP), pid 6328, tgid 6328 (syz-executor), ts 132604632127, free_ts 133183234936

set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21d5/0x22b0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416

alloc_frozen_pages_noprof mm/mempolicy.c:2487 [inline]
alloc_pages_noprof+0xa9/0x190 mm/mempolicy.c:2507
pagetable_alloc_noprof include/linux/mm.h:2881 [inline]
__pte_alloc_one_noprof include/asm-generic/pgalloc.h:75 [inline]
pte_alloc_one+0x21/0x170 arch/x86/mm/pgtable.c:18
__pte_alloc+0x25/0x1a0 mm/memory.c:452
copy_pte_range mm/memory.c:1107 [inline]
copy_pmd_range+0x6a91/0x71d0 mm/memory.c:1261
copy_pud_range mm/memory.c:1298 [inline]
copy_p4d_range mm/memory.c:1322 [inline]
copy_page_range+0xc14/0x1270 mm/memory.c:1410
dup_mmap+0xf57/0x1ac0 mm/mmap.c:1834
dup_mm kernel/fork.c:1485 [inline]
copy_mm+0x13c/0x4b0 kernel/fork.c:1537
copy_process+0x1706/0x3c00 kernel/fork.c:2179
kernel_clone+0x224/0x7c0 kernel/fork.c:2609
__do_sys_clone kernel/fork.c:2752 [inline]
__se_sys_clone kernel/fork.c:2736 [inline]
__x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2736

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

page last free pid 920 tgid 920 stack trace:

reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbb1/0xd20 mm/page_alloc.c:2895

pagetable_free include/linux/mm.h:2898 [inline]
pagetable_dtor_free include/linux/mm.h:2996 [inline]
__tlb_remove_table+0x2d2/0x3b0 include/asm-generic/tlb.h:220
__tlb_remove_table_free mm/mmu_gather.c:227 [inline]
tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:290
rcu_do_batch kernel/rcu/tree.c:2605 [inline]
rcu_core+0xca8/0x1770 kernel/rcu/tree.c:2861
handle_softirqs+0x286/0x870 kernel/softirq.c:579
__do_softirq kernel/softirq.c:613 [inline]
invoke_softirq kernel/softirq.c:453 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
instr_sysvec_call_function_single arch/x86/kernel/smp.c:266 [inline]
sysvec_call_function_single+0xa3/0xc0 arch/x86/kernel/smp.c:266
asm_sysvec_call_function_single+0x1a/0x20 arch/x86/include/asm/idtentry.h:709

Memory state around the buggy address:

ffff888078dca200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888078dca280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888078dca300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888078dca380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888078dca400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit: 755fa5b4 Merge tag 'cgroup-for-6.18' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14fea42c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9c0c1e13e3c8731f

dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=16fb6942580000

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:

KASAN: slab-out-of-bounds Read in ext4_find_extent

EXT4-fs (loop4): stripe (1570) is not aligned with cluster size (16), stripe is disabled
==================================================================
BUG: KASAN: slab-out-of-bounds in ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
BUG: KASAN: slab-out-of-bounds in ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
Read of size 4 at addr ffff8880739bce18 by task syz.4.64/6825

CPU: 1 UID: 0 PID: 6825 Comm: syz.4.64 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595

ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956

ext4_ext_map_blocks+0x27c/0x3880 fs/ext4/extents.c:4211

ext4_map_query_blocks+0x13b/0x930 fs/ext4/inode.c:550
ext4_map_blocks+0x4b3/0x1740 fs/ext4/inode.c:773

_ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943
ext4_block_write_begin+0x990/0x1710 fs/ext4/inode.c:1198
ext4_write_begin+0xc04/0x19a0 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x445/0xda0 fs/ext4/inode.c:3129
generic_perform_write+0x2c2/0x900 mm/filemap.c:4175
ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]

vfs_write+0x5c9/0xb30 fs/read_write.c:686

ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f105318e969

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f1054026038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f10533b5fa0 RCX: 00007f105318e969

RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004

RBP: 00007f1053210ab1 R08: 0000000000000000 R09: 0000000000000000

R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 00007f10533b5fa0 R15: 00007ffeabbc1e38
</TASK>

Allocated by task 6341:

kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4376 [inline]
__kmalloc_noprof+0x27a/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]

kzalloc_noprof include/linux/slab.h:1039 [inline]
__register_sysctl_table+0x72/0x1340 fs/proc/proc_sysctl.c:1379
__addrconf_sysctl_register+0x328/0x4c0 net/ipv6/addrconf.c:7321
addrconf_sysctl_register+0x168/0x1c0 net/ipv6/addrconf.c:7369
ipv6_add_dev+0xd46/0x1370 net/ipv6/addrconf.c:460
addrconf_notify+0x794/0x1010 net/ipv6/addrconf.c:3650
notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
call_netdevice_notifiers net/core/dev.c:2281 [inline]
register_netdevice+0x1608/0x1ae0 net/core/dev.c:11244
register_netdev+0x40/0x60 net/core/dev.c:11322
sit_init_net+0x228/0x5c0 net/ipv6/sit.c:1867
ops_init+0x359/0x5c0 net/core/net_namespace.c:137
setup_net+0xfe/0x320 net/core/net_namespace.c:445
copy_net_ns+0x34e/0x4e0 net/core/net_namespace.c:580
create_new_namespaces+0x3f3/0x720 kernel/nsproxy.c:110
unshare_nsproxy_namespaces+0x11c/0x170 kernel/nsproxy.c:218
ksys_unshare+0x4c8/0x8c0 kernel/fork.c:3132
__do_sys_unshare kernel/fork.c:3203 [inline]
__se_sys_unshare kernel/fork.c:3201 [inline]
__x64_sys_unshare+0x38/0x50 kernel/fork.c:3201

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880739bc000
which belongs to the cache kmalloc-cg-4k of size 4096
The buggy address is located 1504 bytes to the right of
allocated 2104-byte region [ffff8880739bc000, ffff8880739bc838)

The buggy address belongs to the physical page:

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x739b8

head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0

memcg:ffff888027c52441

flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)

raw: 00fff00000000040 ffff88801a04b500 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000040004 00000000f5000000 ffff888027c52441
head: 00fff00000000040 ffff88801a04b500 dead000000000122 0000000000000000
head: 0000000000000000 0000000000040004 00000000f5000000 ffff888027c52441
head: 00fff00000000003 ffffea0001ce6e01 00000000ffffffff 00000000ffffffff

head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008

page dumped because: kasan: bad access detected

page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6341, tgid 6341 (syz-executor), ts 124779228140, free_ts 121882435080

set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21d5/0x22b0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416

alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2660
new_slab mm/slub.c:2714 [inline]
___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
__slab_alloc mm/slub.c:3992 [inline]
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]
__kmalloc_cache_noprof+0x296/0x3d0 mm/slub.c:4402
kmalloc_noprof include/linux/slab.h:905 [inline]

kzalloc_noprof include/linux/slab.h:1039 [inline]
snmp6_alloc_dev net/ipv6/addrconf.c:362 [inline]
ipv6_add_dev+0x6ca/0x1370 net/ipv6/addrconf.c:413
addrconf_notify+0x794/0x1010 net/ipv6/addrconf.c:3650
notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
call_netdevice_notifiers net/core/dev.c:2281 [inline]
register_netdevice+0x1608/0x1ae0 net/core/dev.c:11244
register_netdev+0x40/0x60 net/core/dev.c:11322
sit_init_net+0x228/0x5c0 net/ipv6/sit.c:1867
ops_init+0x359/0x5c0 net/core/net_namespace.c:137
setup_net+0xfe/0x320 net/core/net_namespace.c:445
copy_net_ns+0x34e/0x4e0 net/core/net_namespace.c:580
page last free pid 6267 tgid 6267 stack trace:

reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbb1/0xd20 mm/page_alloc.c:2895

vfree+0x25a/0x400 mm/vmalloc.c:3434
kcov_put kernel/kcov.c:439 [inline]
kcov_close+0x28/0x50 kernel/kcov.c:535
__fput+0x44c/0xa70 fs/file_table.c:468
task_work_run+0x1d1/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x2300 kernel/exit.c:961
do_group_exit+0x21c/0x2d0 kernel/exit.c:1102
get_signal+0x125e/0x1310 kernel/signal.c:3034
arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:

ffff8880739bcd00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880739bcd80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880739bce00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8880739bce80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880739bcf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


Tested on:

commit: 22bdd6e6 Merge tag 'x86_apic_for_v6.18_rc1' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=134485cd980000
kernel config: https://syzkaller.appspot.com/x/.config?x=6899ea2dd30a3ed1

dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=114e8260580000

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:

general protection fault in ext4_ext_map_blocks

EXT4-fs (loop1): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
Oops: general protection fault, probably for non-canonical address 0xdffffc000000000a: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057]
CPU: 1 UID: 0 PID: 6473 Comm: syz.1.17 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025

RIP: 0010:ext4_ext_map_blocks+0x2a1/0x38f0 fs/ext4/extents.c:4212
Code: 24 58 45 0f b7 3f 31 ff 44 89 fe e8 59 a6 51 ff 45 85 ff 74 29 e8 af a2 51 ff 4b 8d 1c 7f c1 e3 04 48 83 c3 20 89 d8 c1 e8 03 <42> 80 3c 30 00 74 08 48 89 df e8 f0 10 b5 ff 48 8b 1b eb 0c e8 86
RSP: 0018:ffffc90003e8f060 EFLAGS: 00010206
RAX: 000000000000000a RBX: 0000000000000050 RCX: ffff88807cc91e40
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc90003e8f270 R08: ffffffff8f5ae037 R09: 1ffffffff1eb5c06
R10: dffffc0000000000 R11: fffffbfff1eb5c07 R12: ffffc90003e8f460
R13: 1ffff920007d1e24 R14: dffffc0000000000 R15: 0000000000000001
FS: 00007f8b97f5d6c0(0000) GS:ffff8881264d6000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000004000 CR3: 000000007a25c000 CR4: 00000000003526f0
Call Trace:
<TASK>

ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
ext4_map_blocks+0x860/0x1740 fs/ext4/inode.c:811

_ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943
ext4_block_write_begin+0x990/0x1710 fs/ext4/inode.c:1198
ext4_write_begin+0xc04/0x19a0 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x445/0xda0 fs/ext4/inode.c:3129
generic_perform_write+0x2c2/0x900 mm/filemap.c:4175
ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f8b9718e969

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f8b97f5d038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f8b973b5fa0 RCX: 00007f8b9718e969

RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004

RBP: 00007f8b97210ab1 R08: 0000000000000000 R09: 0000000000000000

R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 00007f8b973b5fa0 R15: 00007ffea2f11788
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_ext_map_blocks+0x2a1/0x38f0 fs/ext4/extents.c:4212
Code: 24 58 45 0f b7 3f 31 ff 44 89 fe e8 59 a6 51 ff 45 85 ff 74 29 e8 af a2 51 ff 4b 8d 1c 7f c1 e3 04 48 83 c3 20 89 d8 c1 e8 03 <42> 80 3c 30 00 74 08 48 89 df e8 f0 10 b5 ff 48 8b 1b eb 0c e8 86
RSP: 0018:ffffc90003e8f060 EFLAGS: 00010206
RAX: 000000000000000a RBX: 0000000000000050 RCX: ffff88807cc91e40
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc90003e8f270 R08: ffffffff8f5ae037 R09: 1ffffffff1eb5c06
R10: dffffc0000000000 R11: fffffbfff1eb5c07 R12: ffffc90003e8f460
R13: 1ffff920007d1e24 R14: dffffc0000000000 R15: 0000000000000001
FS: 00007f8b97f5d6c0(0000) GS:ffff8881263d6000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555839b2c950 CR3: 000000007a25c000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 24 58 and $0x58,%al
2: 45 0f b7 3f movzwl (%r15),%r15d
6: 31 ff xor %edi,%edi
8: 44 89 fe mov %r15d,%esi
b: e8 59 a6 51 ff call 0xff51a669
10: 45 85 ff test %r15d,%r15d
13: 74 29 je 0x3e
15: e8 af a2 51 ff call 0xff51a2c9
1a: 4b 8d 1c 7f lea (%r15,%r15,2),%rbx
1e: c1 e3 04 shl $0x4,%ebx
21: 48 83 c3 20 add $0x20,%rbx
25: 89 d8 mov %ebx,%eax
27: c1 e8 03 shr $0x3,%eax
* 2a: 42 80 3c 30 00 cmpb $0x0,(%rax,%r14,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 48 89 df mov %rbx,%rdi
34: e8 f0 10 b5 ff call 0xffb51129
39: 48 8b 1b mov (%rbx),%rbx
3c: eb 0c jmp 0x4a
3e: e8 .byte 0xe8
3f: 86 .byte 0x86

Tested on:

commit: 22bdd6e6 Merge tag 'x86_apic_for_v6.18_rc1' of git://g..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=1664d05b980000

kernel config: https://syzkaller.appspot.com/x/.config?x=6899ea2dd30a3ed1
dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=14057c14580000

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:

KASAN: slab-out-of-bounds Read in ext4_ext_insert_extent

EXT4-fs (loop4): stripe (1570) is not aligned with cluster size (16), stripe is disabled
==================================================================

BUG: KASAN: slab-out-of-bounds in ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2096
Read of size 4 at addr ffff88805b641c18 by task syz.4.165/7385

CPU: 0 UID: 0 PID: 7385 Comm: syz.4.165 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025

Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595

ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2096
ext4_ext_map_blocks+0x1bc9/0x3890 fs/ext4/extents.c:4420

ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
ext4_map_blocks+0x860/0x1740 fs/ext4/inode.c:811
_ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943

ext4_block_write_begin+0x993/0x1710 fs/ext4/inode.c:1198

ext4_write_begin+0xc04/0x19a0 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x445/0xda0 fs/ext4/inode.c:3129
generic_perform_write+0x2c2/0x900 mm/filemap.c:4175
ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7fbff2b8e969

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007fbff3a58038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007fbff2db5fa0 RCX: 00007fbff2b8e969

RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004

RBP: 00007fbff2c10ab1 R08: 0000000000000000 R09: 0000000000000000

R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 00007fbff2db5fa0 R15: 00007ffc69cdac78
</TASK>

Allocated by task 6339:

kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4376 [inline]

__kvmalloc_node_noprof+0x30d/0x5f0 mm/slub.c:5067
alloc_netdev_mqs+0xa3/0x11b0 net/core/dev.c:11812
rtnl_create_link+0x31f/0xd10 net/core/rtnetlink.c:3633
rtnl_newlink_create+0x25c/0xb00 net/core/rtnetlink.c:3815
__rtnl_newlink net/core/rtnetlink.c:3942 [inline]
rtnl_newlink+0x16d6/0x1c70 net/core/rtnetlink.c:4057
rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6946
netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:714 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:729
__sys_sendto+0x3bd/0x520 net/socket.c:2231
__do_sys_sendto net/socket.c:2238 [inline]
__se_sys_sendto net/socket.c:2234 [inline]
__x64_sys_sendto+0xde/0x100 net/socket.c:2234

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88805b640000

which belongs to the cache kmalloc-cg-4k of size 4096

The buggy address is located 3696 bytes to the right of
allocated 3496-byte region [ffff88805b640000, ffff88805b640da8)

The buggy address belongs to the physical page:

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5b640

head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0

memcg:ffff88802ed031c1

flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a04b500 dead000000000122 0000000000000000

raw: 0000000000000000 0000000000040004 00000000f5000000 ffff88802ed031c1

head: 00fff00000000040 ffff88801a04b500 dead000000000122 0000000000000000

head: 0000000000000000 0000000000040004 00000000f5000000 ffff88802ed031c1
head: 00fff00000000003 ffffea00016d9001 00000000ffffffff 00000000ffffffff

head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated

page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd60c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6339, tgid 6339 (syz-executor), ts 122638337757, free_ts 82614727744

set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21d5/0x22b0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2660
new_slab mm/slub.c:2714 [inline]
___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
__slab_alloc mm/slub.c:3992 [inline]
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]

__do_kmalloc_node mm/slub.c:4375 [inline]
__kvmalloc_node_noprof+0x429/0x5f0 mm/slub.c:5067
alloc_netdev_mqs+0xa3/0x11b0 net/core/dev.c:11812
rtnl_create_link+0x31f/0xd10 net/core/rtnetlink.c:3633
rtnl_newlink_create+0x25c/0xb00 net/core/rtnetlink.c:3815
__rtnl_newlink net/core/rtnetlink.c:3942 [inline]
rtnl_newlink+0x16d6/0x1c70 net/core/rtnetlink.c:4057
rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6946
netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:714 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:729
page last free pid 5876 tgid 5876 stack trace:

reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbb1/0xd20 mm/page_alloc.c:2895
vfree+0x25a/0x400 mm/vmalloc.c:3434
kcov_put kernel/kcov.c:439 [inline]
kcov_close+0x28/0x50 kernel/kcov.c:535
__fput+0x44c/0xa70 fs/file_table.c:468
task_work_run+0x1d1/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x2300 kernel/exit.c:961
do_group_exit+0x21c/0x2d0 kernel/exit.c:1102
get_signal+0x125e/0x1310 kernel/signal.c:3034
arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:

ffff88805b641b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88805b641b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805b641c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88805b641c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88805b641d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Tested on:

commit: 22bdd6e6 Merge tag 'x86_apic_for_v6.18_rc1' of git://g..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=108366e2580000

kernel config: https://syzkaller.appspot.com/x/.config?x=6899ea2dd30a3ed1
dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=13088092580000

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:

KASAN: slab-use-after-free Read in ext4_ext_insert_extent

==================================================================
BUG: KASAN: slab-use-after-free in ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2096
Read of size 4 at addr ffff888044a48c18 by task syz.1.185/7323

CPU: 0 UID: 0 PID: 7323 Comm: syz.1.185 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2096

ext4_ext_map_blocks+0xf2d/0x2890 fs/ext4/extents.c:4420

ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
ext4_map_blocks+0x860/0x1740 fs/ext4/inode.c:811
_ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943

ext4_block_write_begin+0x990/0x1710 fs/ext4/inode.c:1198

ext4_write_begin+0xc04/0x19a0 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x445/0xda0 fs/ext4/inode.c:3129
generic_perform_write+0x2c2/0x900 mm/filemap.c:4175
ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_pwrite64 fs/read_write.c:793 [inline]
__do_sys_pwrite64 fs/read_write.c:801 [inline]
__se_sys_pwrite64 fs/read_write.c:798 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:798
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f35f338e969

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f35f42db038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f35f35b5fa0 RCX: 00007f35f338e969

RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004

RBP: 00007f35f3410ab1 R08: 0000000000000000 R09: 0000000000000000

R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 00007f35f35b5fa0 R15: 00007ffcbdfba708
</TASK>

Allocated by task 6265:

kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4376 [inline]

__kmalloc_noprof+0x27a/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]

tomoyo_realpath_from_path+0xe3/0x5d0 security/tomoyo/realpath.c:251
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]

tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
security_inode_getattr+0x12f/0x330 security/security.c:2416

vfs_getattr fs/stat.c:259 [inline]
vfs_statx_path fs/stat.c:299 [inline]
vfs_statx+0x18e/0x550 fs/stat.c:356
vfs_fstatat+0x118/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat fs/stat.c:536 [inline]
__x64_sys_newfstatat+0x116/0x190 fs/stat.c:536

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6265:

kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68

kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:243 [inline]
__kasan_slab_free+0x5b/0x80 mm/kasan/common.c:275
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2422 [inline]
slab_free mm/slub.c:4695 [inline]
kfree+0x18e/0x440 mm/slub.c:4894
tomoyo_realpath_from_path+0x598/0x5d0 security/tomoyo/realpath.c:286
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]

tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
security_inode_getattr+0x12f/0x330 security/security.c:2416

vfs_getattr fs/stat.c:259 [inline]
vfs_statx_path fs/stat.c:299 [inline]
vfs_statx+0x18e/0x550 fs/stat.c:356
vfs_fstatat+0x118/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat fs/stat.c:536 [inline]
__x64_sys_newfstatat+0x116/0x190 fs/stat.c:536

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888044a48000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 3096 bytes inside of
freed 4096-byte region [ffff888044a48000, ffff888044a49000)

The buggy address belongs to the physical page:

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x44a48

head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0

flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)

raw: 00fff00000000040 ffff88801a042140 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a042140 dead000000000122 0000000000000000
head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0001129201 00000000ffffffff 00000000ffffffff

head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated

page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6265, tgid 6265 (syz-executor), ts 162534949588, free_ts 162514529707

set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21d5/0x22b0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2660
new_slab mm/slub.c:2714 [inline]
___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
__slab_alloc mm/slub.c:3992 [inline]
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]
__do_kmalloc_node mm/slub.c:4375 [inline]

__kmalloc_noprof+0x305/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]

tomoyo_realpath_from_path+0xe3/0x5d0 security/tomoyo/realpath.c:251
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]

tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
security_inode_getattr+0x12f/0x330 security/security.c:2416

vfs_getattr fs/stat.c:259 [inline]
vfs_statx_path fs/stat.c:299 [inline]
vfs_statx+0x18e/0x550 fs/stat.c:356
vfs_fstatat+0x118/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat fs/stat.c:536 [inline]
__x64_sys_newfstatat+0x116/0x190 fs/stat.c:536

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

page last free pid 5185 tgid 5185 stack trace:

reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbb1/0xd20 mm/page_alloc.c:2895

discard_slab mm/slub.c:2758 [inline]
__put_partials+0x156/0x1a0 mm/slub.c:3223
put_cpu_partial+0x17c/0x250 mm/slub.c:3298
__slab_free+0x2d5/0x3c0 mm/slub.c:4565
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:340
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4191 [inline]
slab_alloc_node mm/slub.c:4240 [inline]
__do_kmalloc_node mm/slub.c:4375 [inline]
__kmalloc_noprof+0x224/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]

tomoyo_realpath_from_path+0xe3/0x5d0 security/tomoyo/realpath.c:251
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]

tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
security_inode_getattr+0x12f/0x330 security/security.c:2416
vfs_getattr fs/stat.c:259 [inline]
vfs_fstat fs/stat.c:281 [inline]
__do_sys_newfstat fs/stat.c:555 [inline]
__se_sys_newfstat fs/stat.c:550 [inline]
__x64_sys_newfstat+0xfc/0x200 fs/stat.c:550

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:

ffff888044a48b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888044a48b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888044a48c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888044a48c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888044a48d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


Tested on:

commit: 4b81e2eb Merge tag 'timers-vdso-2025-09-29' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11af6942580000
kernel config: https://syzkaller.appspot.com/x/.config?x=cb6d0df33502bde3

dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=134f6942580000