Re: [PATCH] io_uring: fix NULL pointer dereference for async cancel close

[Pavel Begunkov <asml.silence@gmail.com>]

On 18/01/2021 09:50, Joseph Qi wrote:
> Abaci reported the following crash:
> 
> [   31.252589] BUG: kernel NULL pointer dereference, address: 00000000000000d8
> [   31.253942] #PF: supervisor read access in kernel mode
> [   31.254945] #PF: error_code(0x0000) - not-present page
> [   31.255964] PGD 800000010b76f067 P4D 800000010b76f067 PUD 10b462067 PMD 0
> [   31.257221] Oops: 0000 [#1] SMP PTI
> [   31.257923] CPU: 1 PID: 1788 Comm: io_uring-sq Not tainted 5.11.0-rc4 #1
> [   31.259175] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> [   31.260232] RIP: 0010:__lock_acquire+0x19d/0x18c0
> [   31.261144] Code: 00 00 8b 1d fd 56 dd 08 85 db 0f 85 43 05 00 00 48 c7 c6 98 7b 95 82 48 c7 c7 57 96 93 82 e8 9a bc f5 ff 0f 0b e9 2b 05 00 00 <48> 81 3f c0 ca 67 8a b8 00 00 00 00 41 0f 45 c0 89 04 24 e9 81 fe
> [   31.264297] RSP: 0018:ffffc90001933828 EFLAGS: 00010002
> [   31.265320] RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000000
> [   31.266594] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000000d8
> [   31.267922] RBP: 0000000000000246 R08: 0000000000000001 R09: 0000000000000000
> [   31.269262] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [   31.270550] R13: 0000000000000000 R14: ffff888106e8a140 R15: 00000000000000d8
> [   31.271760] FS:  0000000000000000(0000) GS:ffff88813bd00000(0000) knlGS:0000000000000000
> [   31.273269] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   31.274330] CR2: 00000000000000d8 CR3: 0000000106efa004 CR4: 00000000003706e0
> [   31.275613] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [   31.276855] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [   31.278065] Call Trace:
> [   31.278649]  lock_acquire+0x31a/0x440
> [   31.279404]  ? close_fd_get_file+0x39/0x160
> [   31.280276]  ? __lock_acquire+0x647/0x18c0
> [   31.281112]  _raw_spin_lock+0x2c/0x40
> [   31.281821]  ? close_fd_get_file+0x39/0x160
> [   31.282586]  close_fd_get_file+0x39/0x160
> [   31.283338]  io_issue_sqe+0x1334/0x14e0
> [   31.284053]  ? lock_acquire+0x31a/0x440
> [   31.284763]  ? __io_free_req+0xcf/0x2e0
> [   31.285504]  ? __io_free_req+0x175/0x2e0
> [   31.286247]  ? find_held_lock+0x28/0xb0
> [   31.286968]  ? io_wq_submit_work+0x7f/0x240
> [   31.287733]  io_wq_submit_work+0x7f/0x240
> [   31.288486]  io_wq_cancel_cb+0x161/0x580
> [   31.289230]  ? io_wqe_wake_worker+0x114/0x360
> [   31.290020]  ? io_uring_get_socket+0x40/0x40
> [   31.290832]  io_async_find_and_cancel+0x3b/0x140
> [   31.291676]  io_issue_sqe+0xbe1/0x14e0
> [   31.292405]  ? __lock_acquire+0x647/0x18c0
> [   31.293207]  ? __io_queue_sqe+0x10b/0x5f0
> [   31.293986]  __io_queue_sqe+0x10b/0x5f0
> [   31.294747]  ? io_req_prep+0xdb/0x1150
> [   31.295485]  ? mark_held_locks+0x6d/0xb0
> [   31.296252]  ? mark_held_locks+0x6d/0xb0
> [   31.297019]  ? io_queue_sqe+0x235/0x4b0
> [   31.297774]  io_queue_sqe+0x235/0x4b0
> [   31.298496]  io_submit_sqes+0xd7e/0x12a0
> [   31.299275]  ? _raw_spin_unlock_irq+0x24/0x30
> [   31.300121]  ? io_sq_thread+0x3ae/0x940
> [   31.300873]  io_sq_thread+0x207/0x940
> [   31.301606]  ? do_wait_intr_irq+0xc0/0xc0
> [   31.302396]  ? __ia32_sys_io_uring_enter+0x650/0x650
> [   31.303321]  kthread+0x134/0x180
> [   31.303982]  ? kthread_create_worker_on_cpu+0x90/0x90
> [   31.304886]  ret_from_fork+0x1f/0x30
> 
> This is caused by NULL files when async cancel close, which has
> IO_WQ_WORK_NO_CANCEL set and continue to do work. Fix it by also setting
> needs_files for IORING_OP_ASYNC_CANCEL.

Looks good enough for a quick late-rc fix,
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>

But we need need to rework this NO_CANCEL case for the future. A
reproducer would help much, do you have one? Or even better a liburing
test?

> 
> Reported-by: Abaci <abaci@linux.alibaba.com>
> Cc: stable@vger.kernel.org # 5.6+
> Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> ---
>  fs/io_uring.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 985a9e3..8eb1349 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -883,7 +883,10 @@ struct io_op_def {
>  		.pollin			= 1,
>  		.work_flags		= IO_WQ_WORK_MM | IO_WQ_WORK_FILES,
>  	},
> -	[IORING_OP_ASYNC_CANCEL] = {},
> +	[IORING_OP_ASYNC_CANCEL] = {
> +		/* for async cancel close */
> +		.needs_file		= 1,
> +	},
>  	[IORING_OP_LINK_TIMEOUT] = {
>  		.needs_async_data	= 1,
>  		.async_size		= sizeof(struct io_timeout_data),
> 

-- 
Pavel Begunkov