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Mon, 09 Mar 2026 11:35:28 -0700 (PDT) Message-ID: Date: Mon, 9 Mar 2026 12:35:27 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] io_uring/register.c: fix NULL pointer dereference in io_register_resize_rings From: Jens Axboe To: Linus Torvalds Cc: Hao-Yu Yang , security@kernel.org, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <42AD516A-B078-40A5-94EE-80739B9883E7@kernel.dk> <453563bb-8dda-471a-901a-30ba9ff3f9c8@kernel.dk> Content-Language: en-US In-Reply-To: <453563bb-8dda-471a-901a-30ba9ff3f9c8@kernel.dk> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/9/26 12:34 PM, Jens Axboe wrote: > How about something like this? I don't particularly like using ->flags > for this, as these are otherwise static after the ring has been set up. > Hence it'd be better to to just use a separate value for this, > ->in_resize, and use smp_load_acquire/release. The write side can be as > expensive as we want it to be, as it's not a hot path at all. And the > acquire read should light weight enough here. _actual_ patch, doesn't help if we don't kill the manual atomic_or()... diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h index 3e4a82a6f817..428eb5b2c624 100644 --- a/include/linux/io_uring_types.h +++ b/include/linux/io_uring_types.h @@ -394,6 +394,7 @@ struct io_ring_ctx { atomic_t cq_wait_nr; atomic_t cq_timeouts; struct wait_queue_head cq_wait; + int in_resize; } ____cacheline_aligned_in_smp; /* timeouts */ diff --git a/io_uring/register.c b/io_uring/register.c index 3378014e51fb..048a1dcd9df1 100644 --- a/io_uring/register.c +++ b/io_uring/register.c @@ -575,6 +575,7 @@ static int io_register_resize_rings(struct io_ring_ctx *ctx, void __user *arg) * ctx->mmap_lock as well. Likewise, hold the completion lock over the * duration of the actual swap. */ + smp_store_release(&ctx->in_resize, 1); mutex_lock(&ctx->mmap_lock); spin_lock(&ctx->completion_lock); o.rings = ctx->rings; @@ -647,6 +648,7 @@ static int io_register_resize_rings(struct io_ring_ctx *ctx, void __user *arg) if (ctx->sq_data) io_sq_thread_unpark(ctx->sq_data); + smp_store_release(&ctx->in_resize, 0); return ret; } diff --git a/io_uring/tw.c b/io_uring/tw.c index 1ee2b8ab07c8..3414cb27879a 100644 --- a/io_uring/tw.c +++ b/io_uring/tw.c @@ -152,6 +152,13 @@ void tctx_task_work(struct callback_head *cb) WARN_ON_ONCE(ret); } +static void io_mark_taskrun(struct io_ring_ctx *ctx) +{ + if (ctx->flags & IORING_SETUP_TASKRUN_FLAG && + !smp_load_acquire(&ctx->in_resize)) + atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags); +} + void io_req_local_work_add(struct io_kiocb *req, unsigned flags) { struct io_ring_ctx *ctx = req->ctx; @@ -206,8 +213,7 @@ void io_req_local_work_add(struct io_kiocb *req, unsigned flags) */ if (!head) { - if (ctx->flags & IORING_SETUP_TASKRUN_FLAG) - atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags); + io_mark_taskrun(ctx); if (ctx->has_evfd) io_eventfd_signal(ctx, false); } @@ -231,8 +237,7 @@ void io_req_normal_work_add(struct io_kiocb *req) if (!llist_add(&req->io_task_work.node, &tctx->task_list)) return; - if (ctx->flags & IORING_SETUP_TASKRUN_FLAG) - atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags); + io_mark_taskrun(ctx); /* SQPOLL doesn't need the task_work added, it'll run it itself */ if (ctx->flags & IORING_SETUP_SQPOLL) { -- Jens Axboe