Re: [PATCH] io_uring: validate user-controlled cq.head in io_cqe_cache_refill()

On 5/13/26 12:32 AM, Zizhi Wo wrote:
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 4ed998d60c09..92e255e9e08f 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -710,11 +710,13 @@ static bool io_fill_nop_cqe(struct io_ring_ctx *ctx, unsigned int off)
>   * fill the cq entry
>   */
>  bool io_cqe_cache_refill(struct io_ring_ctx *ctx, bool overflow, bool cqe32)
>  {
>  	struct io_rings *rings = ctx->rings;
> -	unsigned int off = ctx->cached_cq_tail & (ctx->cq_entries - 1);
> +	unsigned int head = READ_ONCE(ctx->rings->cq.head);
> +	unsigned int tail = ctx->cached_cq_tail;
> +	unsigned int off = tail & (ctx->cq_entries - 1);
>  	unsigned int free, queued, len;

This looks wrong, as you're snapshotting 'tail' while it could get
modified by if a nop fill before the refill happens. And fwiw, looks
like the refill part potentially suffers from the same unsigned issue.

-- 
Jens Axboe