Re: [syzbot] KASAN: use-after-free Write in __io_free_req

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: refcount bug in delayed_put_task_struct

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 19 at lib/refcount.c:28 refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted 5.15.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
Code: e9 db fe ff ff 48 89 df e8 7c aa 1a fe e9 8a fe ff ff e8 92 6c d3 fd 48 c7 c7 80 bb be 89 c6 05 95 a4 8d 09 01 e8 5b 36 19 05 <0f> 0b e9 af fe ff ff 0f 1f 84 00 00 00 00 00 41 56 41 55 41 54 55
RSP: 0018:ffffc90000d97d00 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888011af5580 RSI: ffffffff815e8868 RDI: fffff520001b2f92
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815e260e R11: 0000000000000000 R12: ffff888071c45580
R13: ffff888071c455a8 R14: 0000000000000004 R15: ffff888071c46a50
FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe200c24218 CR3: 000000006f2d8000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __refcount_sub_and_test include/linux/refcount.h:283 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 put_task_struct include/linux/sched/task.h:112 [inline]
 delayed_put_task_struct+0x2e3/0x340 kernel/exit.c:172
 rcu_do_batch kernel/rcu/tree.c:2508 [inline]
 rcu_core+0x7ab/0x1470 kernel/rcu/tree.c:2743
 __do_softirq+0x29b/0x9c2 kernel/softirq.c:558
 run_ksoftirqd kernel/softirq.c:920 [inline]
 run_ksoftirqd+0x2d/0x60 kernel/softirq.c:912
 smpboot_thread_fn+0x645/0x9c0 kernel/smpboot.c:164
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295


Tested on:

commit:         3ecd20a9 io-wq: remove worker to owner tw dependency
git tree:       https://github.com/isilence/linux.git syz-test-iofree
console output: https://syzkaller.appspot.com/x/log.txt?x=160209d4b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=10c050a45aafafcc
dashboard link: https://syzkaller.appspot.com/bug?extid=78b76ebc91042904f34e
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2