[syzbot] [io-uring?] KASAN: slab-use-after-free Read in __io_req_task_work_add (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8b789f2b7602 Merge tag 'mm-hotfixes-stable-2025-09-17-21-1..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10154f62580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4d8792ecb6308d0f
dashboard link: https://syzkaller.appspot.com/bug?extid=baa2e0f4e02df602583e
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2c5815e2639f/disk-8b789f2b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1e6e9e88f96c/vmlinux-8b789f2b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e1f2a1d87f1f/bzImage-8b789f2b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+baa2e0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in io_req_local_work_add io_uring/io_uring.c:1219 [inline]
BUG: KASAN: slab-use-after-free in __io_req_task_work_add+0x589/0x950 io_uring/io_uring.c:1287
Read of size 4 at addr ffff888032ab9904 by task iou-wrk-12380/12382

CPU: 0 UID: 0 PID: 12382 Comm: iou-wrk-12380 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
io_req_local_work_add io_uring/io_uring.c:1219 [inline]
__io_req_task_work_add+0x589/0x950 io_uring/io_uring.c:1287
io_req_task_work_add io_uring/io_uring.h:157 [inline]
io_req_complete_post io_uring/io_uring.c:961 [inline]
io_issue_sqe+0x643/0xfd0 io_uring/io_uring.c:1802
io_wq_submit_work+0x6e9/0xb90 io_uring/io_uring.c:1908
io_worker_handle_work+0x7cd/0x1180 io_uring/io-wq.c:650
io_wq_worker+0x42f/0xeb0 io_uring/io-wq.c:704
ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 12382:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
unpoison_slab_object mm/kasan/common.c:330 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:356
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]
kmem_cache_alloc_noprof+0x1c1/0x3c0 mm/slub.c:4247
io_msg_get_kiocb io_uring/msg_ring.c:117 [inline]
io_msg_data_remote io_uring/msg_ring.c:126 [inline]
__io_msg_ring_data+0x47b/0xa80 io_uring/msg_ring.c:151
io_msg_ring_data io_uring/msg_ring.c:173 [inline]
io_msg_ring+0x134/0xa00 io_uring/msg_ring.c:314
__io_issue_sqe+0x17e/0x4b0 io_uring/io_uring.c:1773
io_issue_sqe+0x165/0xfd0 io_uring/io_uring.c:1796
io_wq_submit_work+0x6e9/0xb90 io_uring/io_uring.c:1908
io_worker_handle_work+0x7cd/0x1180 io_uring/io-wq.c:650
io_wq_worker+0x42f/0xeb0 io_uring/io-wq.c:704
ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 12380:
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_mempool_poison_object+0xad/0x130 mm/kasan/common.c:533
kasan_mempool_poison_object include/linux/kasan.h:360 [inline]
io_alloc_cache_put io_uring/alloc_cache.h:23 [inline]
io_msg_tw_complete+0x12c/0x4f0 io_uring/msg_ring.c:80
__io_run_local_work_loop io_uring/io_uring.c:1330 [inline]
__io_run_local_work+0x350/0x810 io_uring/io_uring.c:1363
io_run_local_work_locked io_uring/io_uring.c:1385 [inline]
__do_sys_io_uring_enter io_uring/io_uring.c:3478 [inline]
__se_sys_io_uring_enter+0x1725/0x2b20 io_uring/io_uring.c:3399
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
__do_fast_syscall_32+0xb6/0x2b0 arch/x86/entry/syscall_32.c:306
do_fast_syscall_32+0x34/0x80 arch/x86/entry/syscall_32.c:331
entry_SYSENTER_compat_after_hwframe+0x84/0x8e

The buggy address belongs to the object at ffff888032ab98c0
which belongs to the cache io_kiocb of size 248
The buggy address is located 68 bytes inside of
freed 248-byte region [ffff888032ab98c0, ffff888032ab99b8)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x32ab9
memcg:ffff8880334ee901
ksm flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff8881413b9c80 ffffea0001f63740 dead000000000003
raw: 0000000000000000 00000000800c000c 00000000f5000000 ffff8880334ee901
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 12143, tgid 12142 (syz.1.1033), ts 466289495240, free_ts 459260987318
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+0x21e4/0x22c0 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
__kmem_cache_alloc_bulk mm/slub.c:5346 [inline]
kmem_cache_alloc_bulk_noprof+0x20e/0x790 mm/slub.c:5418
__io_alloc_req_refill+0x9d/0x280 io_uring/io_uring.c:1007
io_alloc_req io_uring/io_uring.h:453 [inline]
io_submit_sqes+0xbfd/0x1d30 io_uring/io_uring.c:2387
__do_sys_io_uring_enter io_uring/io_uring.c:3465 [inline]
__se_sys_io_uring_enter+0x2df/0x2b20 io_uring/io_uring.c:3399
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
__do_fast_syscall_32+0xb6/0x2b0 arch/x86/entry/syscall_32.c:306
do_fast_syscall_32+0x34/0x80 arch/x86/entry/syscall_32.c:331
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
page last free pid 15 tgid 15 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2895
rcu_do_batch kernel/rcu/tree.c:2605 [inline]
rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
handle_softirqs+0x283/0x870 kernel/softirq.c:579
run_ksoftirqd+0x9b/0x100 kernel/softirq.c:968
smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:160
kthread+0x70e/0x8a0 kernel/kthread.c:463
ret_from_fork+0x436/0x7d0 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:
ffff888032ab9800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
ffff888032ab9880: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
>ffff888032ab9900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888032ab9980: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc
ffff888032ab9a00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup