[syzbot] [fs?] KASAN: slab-use-after-free Read in clear_tfile_check_list

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 80dd246accce Add linux-next specific files for 20260518
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17ca9fba580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2a0b5969e136a632
dashboard link: https://syzkaller.appspot.com/bug?extid=69a3d7738ad3aa175caf
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=1598082e580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17ac6596580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5e187606d6dc/disk-80dd246a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/96a72e613393/vmlinux-80dd246a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c2905548782c/bzImage-80dd246a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+69a3d7...@syzkaller.appspotmail.com

RAX: ffffffffffffffda RBX: 00007f129c6a5fa0 RCX: 00007f129c42ce59
RDX: 0000000000000005 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00007ffeb1d5c4f0 R08: 0000000000000000 R09: 0000000000000000
R10: 00002000000004c0 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f129c6a5fac R14: 00007f129c6a5fa0 R15: 00007f129c6a5fa0
</TASK>
==================================================================
BUG: KASAN: slab-use-after-free in clear_tfile_check_list+0x114/0x380 fs/eventpoll.c:2443
Read of size 8 at addr ffff88803f021568 by task syz.0.74/5985

CPU: 1 UID: 0 PID: 5985 Comm: syz.0.74 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description+0x55/0x1e0 mm/kasan/report.c:378
print_report+0x58/0x70 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
clear_tfile_check_list+0x114/0x380 fs/eventpoll.c:2443
do_epoll_ctl_file+0x8fd/0xed0 fs/eventpoll.c:-1
do_epoll_ctl fs/eventpoll.c:2698 [inline]
__do_sys_epoll_ctl fs/eventpoll.c:2715 [inline]
__se_sys_epoll_ctl+0x14e/0x210 fs/eventpoll.c:2706
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f129c42ce59
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:00007ffeb1d5c488 EFLAGS: 00000246 ORIG_RAX: 00000000000000e9
RAX: ffffffffffffffda RBX: 00007f129c6a5fa0 RCX: 00007f129c42ce59
RDX: 0000000000000005 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00007ffeb1d5c4f0 R08: 0000000000000000 R09: 0000000000000000
R10: 00002000000004c0 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f129c6a5fac R14: 00007f129c6a5fa0 R15: 00007f129c6a5fa0
</TASK>

Allocated by task 5985:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
unpoison_slab_object mm/kasan/common.c:340 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4583 [inline]
slab_alloc_node mm/slub.c:4912 [inline]
kmem_cache_alloc_noprof+0x33b/0x680 mm/slub.c:4919
ep_attach_file fs/eventpoll.c:1751 [inline]
ep_register_epitem fs/eventpoll.c:1833 [inline]
ep_insert+0x512/0x1820 fs/eventpoll.c:1876
do_epoll_ctl_file+0x8bb/0xed0 fs/eventpoll.c:2651
do_epoll_ctl fs/eventpoll.c:2698 [inline]
__do_sys_epoll_ctl fs/eventpoll.c:2715 [inline]
__se_sys_epoll_ctl+0x14e/0x210 fs/eventpoll.c:2706
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5985:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2700 [inline]
slab_free mm/slub.c:6284 [inline]
kmem_cache_free+0x187/0x6c0 mm/slub.c:6411
ep_remove+0x155/0x2a0 fs/eventpoll.c:1135
ep_insert+0x1372/0x1820 fs/eventpoll.c:-1
do_epoll_ctl_file+0x8bb/0xed0 fs/eventpoll.c:2651
do_epoll_ctl fs/eventpoll.c:2698 [inline]
__do_sys_epoll_ctl fs/eventpoll.c:2715 [inline]
__se_sys_epoll_ctl+0x14e/0x210 fs/eventpoll.c:2706
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88803f021560
which belongs to the cache ep_head of size 16
The buggy address is located 8 bytes inside of
freed 16-byte region [ffff88803f021560, ffff88803f021570)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88803f0213e0 pfn:0x3f021
memcg:ffff88803d044001
flags: 0x80000000000200(workingset|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000200 ffff888140419c80 ffffea0000a5dc90 ffff888020ecdf88
raw: ffff88803f0213e0 0000000800800078 00000000f5000000 ffff88803d044001
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 4982, tgid 4982 (udevd), ts 45918061529, free_ts 45769000837
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1873
prep_new_page mm/page_alloc.c:1881 [inline]
get_page_from_freelist+0x27d6/0x2850 mm/page_alloc.c:3954
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5297
alloc_slab_page mm/slub.c:3289 [inline]
allocate_slab+0x74/0x5e0 mm/slub.c:3404
new_slab mm/slub.c:3447 [inline]
refill_objects+0x33c/0x3d0 mm/slub.c:7226
refill_sheaf mm/slub.c:2827 [inline]
__pcs_replace_empty_main+0x373/0x720 mm/slub.c:4665
alloc_from_pcs mm/slub.c:4763 [inline]
slab_alloc_node mm/slub.c:4897 [inline]
kmem_cache_alloc_noprof+0x433/0x680 mm/slub.c:4919
ep_attach_file fs/eventpoll.c:1751 [inline]
ep_register_epitem fs/eventpoll.c:1833 [inline]
ep_insert+0x512/0x1820 fs/eventpoll.c:1876
do_epoll_ctl_file+0x8bb/0xed0 fs/eventpoll.c:2651
do_epoll_ctl fs/eventpoll.c:2698 [inline]
__do_sys_epoll_ctl fs/eventpoll.c:2715 [inline]
__se_sys_epoll_ctl+0x14e/0x210 fs/eventpoll.c:2706
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 21 tgid 21 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1420 [inline]
__free_frozen_pages+0x1075/0x11b0 mm/page_alloc.c:2958
__tlb_remove_table_free mm/mmu_gather.c:228 [inline]
tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:299
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core kernel/rcu/tree.c:2869 [inline]
rcu_cpu_kthread+0x99e/0x1470 kernel/rcu/tree.c:2957
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x389/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
ffff88803f021400: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
ffff88803f021480: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
>ffff88803f021500: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
^
ffff88803f021580: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
ffff88803f021600: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
==================================================================


---
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