[syzbot] [ext4?] KASAN: use-after-free Read in xattr_find_entry (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2961f841b025 Merge tag 'turbostat-2026.02.14' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=156cb15a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=665cbf0979cda6c5
dashboard link: https://syzkaller.appspot.com/bug?extid=fb32afec111a7d61b939
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17a43b3a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=157f895a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/54d6a30cbc5f/disk-2961f841.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/40003e4ec76c/vmlinux-2961f841.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2db393aba9ff/bzImage-2961f841.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/07bdbcf04dc1/mount_0.gz
fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=12b95c02580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fb32af...@syzkaller.appspotmail.com

loop0: detected capacity change from 1024 to 64
EXT4-fs error (device loop0): ext4_find_dest_de:2050: inode #12: block 7: comm syz.0.17: bad entry in directory: directory entry overrun - offset=0, inode=268435456, rec_len=1280, size=56 fake=0
==================================================================
BUG: KASAN: use-after-free in xattr_find_entry+0x1a5/0x280 fs/ext4/xattr.c:334
Read of size 4 at addr ffff88806ee29004 by task syz.0.17/5997

CPU: 1 UID: 49663 PID: 5997 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xba/0x230 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
xattr_find_entry+0x1a5/0x280 fs/ext4/xattr.c:334
ext4_xattr_ibody_get+0x232/0x4c0 fs/ext4/xattr.c:655
ext4_xattr_get+0x123/0x6a0 fs/ext4/xattr.c:709
ext4_get_acl+0x84/0x930 fs/ext4/acl.c:165
__get_acl+0x27e/0x410 fs/posix_acl.c:159
check_acl+0x3a/0x150 fs/namei.c:385
acl_permission_check fs/namei.c:471 [inline]
generic_permission+0x497/0x690 fs/namei.c:524
do_inode_permission fs/namei.c:585 [inline]
inode_permission+0x243/0x5f0 fs/namei.c:648
lookup_inode_permission_may_exec fs/namei.c:-1 [inline]
may_lookup fs/namei.c:1973 [inline]
link_path_walk+0x1149/0x18d0 fs/namei.c:2595
path_lookupat+0xe4/0x8c0 fs/namei.c:2803
filename_lookup+0x256/0x5d0 fs/namei.c:2833
user_path_at+0x40/0x160 fs/namei.c:3612
do_mount fs/namespace.c:4156 [inline]
__do_sys_mount fs/namespace.c:4348 [inline]
__se_sys_mount+0x2dc/0x420 fs/namespace.c:4325
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f72cdd9c629
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff6aba2c28 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f72ce015fa0 RCX: 00007f72cdd9c629
RDX: 0000000000000000 RSI: 0000200000000040 RDI: 0000000000000000
RBP: 00007f72cde32b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000002094080 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f72ce015fac R14: 00007f72ce015fa0 R15: 00007f72ce015fa0
</TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x7f3283789 pfn:0x6ee29
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001bb8a88 ffffea0001bb8908 0000000000000000
raw: 00000007f3283789 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO|__GFP_COMP), pid 5981, tgid 5981 (sed), ts 108386366383, free_ts 108399318838
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x231/0x280 mm/page_alloc.c:1888
prep_new_page mm/page_alloc.c:1896 [inline]
get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3961
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5249
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2485
folio_alloc_mpol_noprof mm/mempolicy.c:2504 [inline]
vma_alloc_folio_noprof+0xea/0x210 mm/mempolicy.c:2539
folio_prealloc mm/memory.c:-1 [inline]
alloc_anon_folio mm/memory.c:5200 [inline]
do_anonymous_page mm/memory.c:5257 [inline]
do_pte_missing+0x1656/0x3750 mm/memory.c:4467
handle_pte_fault mm/memory.c:6308 [inline]
__handle_mm_fault mm/memory.c:6446 [inline]
handle_mm_fault+0x1bec/0x3310 mm/memory.c:6615
do_user_addr_fault+0xa73/0x1340 arch/x86/mm/fault.c:1334
handle_page_fault arch/x86/mm/fault.c:1474 [inline]
exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
page last free pid 5981 tgid 5981 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1432 [inline]
free_unref_folios+0xd38/0x14c0 mm/page_alloc.c:3039
folios_put_refs+0x789/0x8d0 mm/swap.c:1002
free_pages_and_swap_cache+0x2e7/0x5b0 mm/swap_state.c:423
__tlb_batch_free_encoded_pages mm/mmu_gather.c:138 [inline]
tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:398 [inline]
tlb_flush_mmu+0x6d3/0xa30 mm/mmu_gather.c:405
tlb_finish_mmu+0xf9/0x230 mm/mmu_gather.c:530
exit_mmap+0x453/0xdb0 mm/mmap.c:1290
__mmput+0x118/0x430 kernel/fork.c:1174
exit_mm+0x168/0x220 kernel/exit.c:581
do_exit+0x62e/0x2320 kernel/exit.c:959
do_group_exit+0x21b/0x2d0 kernel/exit.c:1112
__do_sys_exit_group kernel/exit.c:1123 [inline]
__se_sys_exit_group kernel/exit.c:1121 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1121
x64_sys_call+0x221a/0x2240 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88806ee28f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88806ee28f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88806ee29000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88806ee29080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88806ee29100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


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