Re: [PATCH] io_uring: Add NULL checks for current->io_uring

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

On 1/11/23 10:19, Jia-Ju Bai wrote:
> As described in a previous commit 998b30c3948e, current->io_uring could
> be NULL, and thus a NULL check is required for this variable.
> 
> In the same way, other functions that access current->io_uring also
> require NULL checks of this variable.

io_uring_enter() {
...
	ret = io_uring_add_tctx_node(ctx);
	if (unlikely(ret))
		goto out;

	mutex_lock(&ctx->uring_lock);
	ret = io_submit_sqes(ctx, to_submit);
}

io_uring_add_tctx_node() should make sure to setup current->io_uring
or fail, so it should be NULL there, and SQPOLL should be fine as well.
Did you see it hitting NULL?


> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
> ---
>   io_uring/io_uring.c | 3 ++-
>   io_uring/io_uring.h | 3 +++
>   io_uring/tctx.c     | 9 ++++++++-
>   3 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 2ac1cd8d23ea..8075c0880c7a 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -2406,7 +2406,8 @@ int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
>   		/* try again if it submitted nothing and can't allocate a req */
>   		if (!ret && io_req_cache_empty(ctx))
>   			ret = -EAGAIN;
> -		current->io_uring->cached_refs += left;
> +		if (likely(current->io_uring))
> +			current->io_uring->cached_refs += left;
>   	}
>   
>   	io_submit_state_end(ctx);
> diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
> index ab4b2a1c3b7e..398c7c2ba22b 100644
> --- a/io_uring/io_uring.h
> +++ b/io_uring/io_uring.h
> @@ -362,6 +362,9 @@ static inline void io_get_task_refs(int nr)
>   {
>   	struct io_uring_task *tctx = current->io_uring;
>   
> +	if (unlikely(!tctx))
> +		return;
> +
>   	tctx->cached_refs -= nr;
>   	if (unlikely(tctx->cached_refs < 0))
>   		io_task_refs_refill(tctx);
> diff --git a/io_uring/tctx.c b/io_uring/tctx.c
> index 4324b1cf1f6a..6574bbe82b5d 100644
> --- a/io_uring/tctx.c
> +++ b/io_uring/tctx.c
> @@ -145,7 +145,8 @@ int __io_uring_add_tctx_node_from_submit(struct io_ring_ctx *ctx)
>   	if (ret)
>   		return ret;
>   
> -	current->io_uring->last = ctx;
> +	if (likely(current->io_uring))
> +		current->io_uring->last = ctx;
>   	return 0;
>   }
>   
> @@ -200,6 +201,9 @@ void io_uring_unreg_ringfd(void)
>   	struct io_uring_task *tctx = current->io_uring;
>   	int i;
>   
> +	if (unlikely(!tctx))
> +		return;
> +
>   	for (i = 0; i < IO_RINGFD_REG_MAX; i++) {
>   		if (tctx->registered_rings[i]) {
>   			fput(tctx->registered_rings[i]);
> @@ -259,6 +263,9 @@ int io_ringfd_register(struct io_ring_ctx *ctx, void __user *__arg,
>   		return ret;
>   
>   	tctx = current->io_uring;
> +	if (unlikely(!tctx))
> +		return -EINVAL;
> +
>   	for (i = 0; i < nr_args; i++) {
>   		int start, end;
>   

-- 
Pavel Begunkov