[Android 5.15] KASAN: slab-out-of-bounds Read in do_split

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7fad219d720d Merge android13-5.15 into android13-5.15-lts
git tree: android13-5.15-lts
console output: https://syzkaller.appspot.com/x/log.txt?x=17f0f3d6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=daefb08bb2811735
dashboard link: https://syzkaller.appspot.com/bug?extid=b7d62b4f5863e6bdcdaf
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=1509e5da580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12311516580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7e1209a70d88/disk-7fad219d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9313bf35ee22/vmlinux-7fad219d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6e63a5a4613d/bzImage-7fad219d.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/6ddc1f46384b/mount_0.gz
fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=16a09d02580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b7d62b...@syzkaller.appspotmail.com

EXT4-fs: Warning: mounting with data=journal disables delayed allocation, dioread_nolock, O_DIRECT and fast_commit support!
EXT4-fs (loop2): encrypted files will use data=ordered instead of data journaling mode
EXT4-fs (loop2): 1 truncate cleaned up
EXT4-fs (loop2): mounted filesystem without journal. Opts: barrier=0x0000000000000006,resuid=0x0000000000000000,barrier=0x0000000000000003,norecovery,block_validity,data_err=abort,,errors=continue. Quota mode: none.
==================================================================
BUG: KASAN: slab-out-of-bounds in dx_move_dirents fs/ext4/namei.c:1935 [inline]
BUG: KASAN: slab-out-of-bounds in do_split+0x132f/0x1fb0 fs/ext4/namei.c:2056
Write of size 24923 at addr ffff88812e156c2a by task syz.2.17/360

CPU: 1 PID: 360 Comm: syz.2.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
__dump_stack+0x21/0x30 lib/dump_stack.c:88
dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:427 [inline]
kasan_report+0xf1/0x140 mm/kasan/report.c:444
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x249/0x2a0 mm/kasan/generic.c:189
memset+0x23/0x40 mm/kasan/shadow.c:44
dx_move_dirents fs/ext4/namei.c:1935 [inline]
do_split+0x132f/0x1fb0 fs/ext4/namei.c:2056
ext4_dx_add_entry+0x54f/0x1620 fs/ext4/namei.c:2688
ext4_add_entry+0xa9c/0x1030 fs/ext4/namei.c:2468
ext4_add_nondir+0x97/0x270 fs/ext4/namei.c:2845
ext4_create+0x2e6/0x470 fs/ext4/namei.c:2891
vfs_create+0x342/0x520 fs/namei.c:3170
do_mknodat+0x334/0x7a0 fs/namei.c:4002
__do_sys_mknod fs/namei.c:4035 [inline]
__se_sys_mknod fs/namei.c:4033 [inline]
__x64_sys_mknod+0x8e/0xa0 fs/namei.c:4033
x64_sys_call+0x886/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:134
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7ff07c7f0819
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:00007fffb8874a58 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
RAX: ffffffffffffffda RBX: 00007ff07ca69fa0 RCX: 00007ff07c7f0819
RDX: 0000000000000247 RSI: 0000000000000010 RDI: 0000200000000340
RBP: 00007ff07c886c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff07ca69fac R14: 00007ff07ca69fa0 R15: 00007ff07ca69fa0
</TASK>

The buggy address belongs to the page:
page:ffffea0004b85580 refcount:2 mapcount:0 mapping:ffff88810930ac98 index:0x8 pfn:0x12e156
memcg:ffff888100256780
aops:def_blk_aops ino:700002
flags: 0x400000000002203e(referenced|uptodate|dirty|lru|active|private|mappedtodisk|zone=1)
raw: 400000000002203e ffffea0004b855c8 ffffea0004b85548 ffff88810930ac98
raw: 0000000000000008 ffff8881092bf348 00000002ffffffff ffff888100256780
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x112c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY|__GFP_HARDWALL), pid 296, ts 24120551797, free_ts 23405833838
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2605
prep_new_page+0x1c/0x110 mm/page_alloc.c:2611
get_page_from_freelist+0x2d3a/0x2dc0 mm/page_alloc.c:4485
__alloc_pages+0x1a2/0x460 mm/page_alloc.c:5822
__alloc_pages_node include/linux/gfp.h:595 [inline]
alloc_pages_node include/linux/gfp.h:609 [inline]
alloc_pages include/linux/gfp.h:622 [inline]
__page_cache_alloc include/linux/pagemap.h:305 [inline]
page_cache_ra_unbounded+0x2d5/0x9a0 mm/readahead.c:227
do_page_cache_ra mm/readahead.c:280 [inline]
force_page_cache_ra+0x3fd/0x460 mm/readahead.c:312
page_cache_sync_ra+0x2b4/0x430 mm/readahead.c:590
page_cache_sync_readahead include/linux/pagemap.h:831 [inline]
filemap_get_pages mm/filemap.c:2569 [inline]
filemap_read+0x694/0x2040 mm/filemap.c:2654
generic_file_read_iter+0xac/0x400 mm/filemap.c:2814
blkdev_read_iter+0x12f/0x160 block/fops.c:563
call_read_iter include/linux/fs.h:2206 [inline]
new_sync_read fs/read_write.c:404 [inline]
vfs_read+0x6c9/0xc40 fs/read_write.c:485
ksys_read+0x149/0x250 fs/read_write.c:623
__do_sys_read fs/read_write.c:633 [inline]
__se_sys_read fs/read_write.c:631 [inline]
__x64_sys_read+0x7b/0x90 fs/read_write.c:631
x64_sys_call+0x96d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1472 [inline]
free_pcp_prepare mm/page_alloc.c:1544 [inline]
free_unref_page_prepare+0x542/0x550 mm/page_alloc.c:3534
free_unref_page+0xae/0x540 mm/page_alloc.c:3616
free_the_page mm/page_alloc.c:805 [inline]
__free_pages+0x6c/0x100 mm/page_alloc.c:5898
__vunmap+0x86d/0xa00 mm/vmalloc.c:2660
__vfree mm/vmalloc.c:2709 [inline]
vfree+0x8b/0xc0 mm/vmalloc.c:2740
kcov_put kernel/kcov.c:417 [inline]
kcov_close+0x2b/0x50 kernel/kcov.c:519
__fput+0x20b/0x8b0 fs/file_table.c:311
____fput+0x15/0x20 fs/file_table.c:339
task_work_run+0x127/0x190 kernel/task_work.c:188
exit_task_work include/linux/task_work.h:33 [inline]
do_exit+0xa9e/0x27e0 kernel/exit.c:889
do_group_exit+0x141/0x310 kernel/exit.c:1003
get_signal+0x66a/0x1480 kernel/signal.c:2907
arch_do_signal_or_restart+0xdf/0x11c0 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307

Memory state around the buggy address:
ffff88812e159f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88812e159f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88812e15a000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88812e15a080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88812e15a100: fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb fb
==================================================================


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