Re: [PATCH 5.11] io_uring: fix files cancellation

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

On 25/11/2020 02:19, Pavel Begunkov wrote:
> io_uring_cancel_files()'s task check condition mistakenly got flipped.
> 
> 1. There can't be a request in the inflight list without
> IO_WQ_WORK_FILES, kill this check to keep the whole condition simpler.
> 2. Also, don't call the function for files==NULL to not do such a check,
> all that staff is already handled well by its counter part,
> __io_uring_cancel_task_requests().
> 
> With that just flip the task check.
> 
> Also, it iowq-cancels all request of current task there, don't forget to
> set right ->files into struct io_task_cancel.> 
> Reported-by: syzbot+c0d52d0b3c0c3ffb9525@syzkaller.appspotmail.com

So, I screwed it just recently and for-5.11. Thanks to syzkaller for 
catching this early.
Just to notice that the reproducer segfaults for me, so I haven't really
reproduced it and needs "syz test" to confirm

> Fixes: c1973b38bf639 ("io_uring: cancel only requests of current task")
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  fs/io_uring.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 7c1f255807f5..f11dc25d975c 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -8725,15 +8725,14 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
>  				  struct files_struct *files)
>  {
>  	while (!list_empty_careful(&ctx->inflight_list)) {
> -		struct io_task_cancel cancel = { .task = task, .files = NULL, };
> +		struct io_task_cancel cancel = { .task = task, .files = files };
>  		struct io_kiocb *req;
>  		DEFINE_WAIT(wait);
>  		bool found = false;
>  
>  		spin_lock_irq(&ctx->inflight_lock);
>  		list_for_each_entry(req, &ctx->inflight_list, inflight_entry) {
> -			if (req->task == task &&
> -			    (req->work.flags & IO_WQ_WORK_FILES) &&
> +			if (req->task != task ||
>  			    req->work.identity->files != files)
>  				continue;
>  			found = true;
> @@ -8805,10 +8804,11 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
>  
>  	io_cancel_defer_files(ctx, task, files);
>  	io_cqring_overflow_flush(ctx, true, task, files);
> -	io_uring_cancel_files(ctx, task, files);
>  
>  	if (!files)
>  		__io_uring_cancel_task_requests(ctx, task);
> +	else
> +		io_uring_cancel_files(ctx, task, files);
>  
>  	if ((ctx->flags & IORING_SETUP_SQPOLL) && ctx->sq_data) {
>  		atomic_dec(&task->io_uring->in_idle);
> 

-- 
Pavel Begunkov