Re: [syzbot] BUG: unable to handle kernel NULL pointer dereference in io_do_iopoll

syzbot
2022-05-17T18:44:17Z

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel NULL pointer dereference in io_do_iopoll

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 0 P4D 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 4077 Comm: syz-executor.0 Not tainted 5.18.0-rc2-syzkaller-00022-ga67f2fc1f9b5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc900056478d8 EFLAGS: 00010246
RAX: ffffffff89dad020 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: 0000000000000003 RSI: ffffc90005647950 RDI: ffff88807f0668c0
RBP: ffff88807f066901 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff81ec0c20 R11: 0000000000000000 R12: 0000000000000003
R13: ffffc90005647950 R14: ffff88807f0668c0 R15: ffff88807f066938
FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000000ba8e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
io_do_iopoll+0x262/0x1080 fs/io_uring.c:2776
io_iopoll_try_reap_events+0xba/0x158 fs/io_uring.c:2829
io_ring_ctx_wait_and_kill+0x1d9/0x327 fs/io_uring.c:10170
io_uring_release+0x42/0x46 fs/io_uring.c:10187
__fput+0x277/0x9d0 fs/file_table.c:317
task_work_run+0xdd/0x1a0 kernel/task_work.c:164
exit_task_work include/linux/task_work.h:37 [inline]
do_exit+0xaff/0x2a00 kernel/exit.c:795
do_group_exit+0xd2/0x2f0 kernel/exit.c:925
get_signal+0x22df/0x24c0 kernel/signal.c:2864
arch_do_signal_or_restart+0x82/0x20f0 arch/x86/kernel/signal.c:867
exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:201
__syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:294
do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fe34b8890e9
Code: Unable to access opcode bytes at RIP 0x7fe34b8890bf.
RSP: 002b:00007fe34c997218 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000001 RBX: 00007fe34b99bf68 RCX: 00007fe34b8890e9
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007fe34b99bf6c
RBP: 00007fe34b99bf60 R08: 00007fff26bf1080 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 00007fe34b99bf6c
R13: 00007fff26becbef R14: 00007fe34c997300 R15: 0000000000022000
</TASK>
Modules linked in:
CR2: 0000000000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffffc900056478d8 EFLAGS: 00010246
RAX: ffffffff89dad020 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: 0000000000000003 RSI: ffffc90005647950 RDI: ffff88807f0668c0
RBP: ffff88807f066901 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff81ec0c20 R11: 0000000000000000 R12: 0000000000000003
R13: ffffc90005647950 R14: ffff88807f0668c0 R15: ffff88807f066938
FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000000ba8e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Tested on:

commit: a67f2fc1 io_uring: don't attempt to IOPOLL for MSG_RIN..
git tree: git://git.kernel.dk/linux-block io_uring-5.18
console output: https://syzkaller.appspot.com/x/log.txt?x=13167865f00000
kernel config: https://syzkaller.appspot.com/x/.config?x=e408a5da421f07d4
dashboard link: https://syzkaller.appspot.com/bug?extid=1a0a53300ce782f8b3ad
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Note: no patches were applied.