FAILED: patch "[PATCH] io_uring: fix task_work add use-after-free with SQPOLL" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x a92193c91e8839fe5fc209616ea95465ae4b919d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026100333-unpicked-popsicle-044c@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a92193c91e8839fe5fc209616ea95465ae4b919d Mon Sep 17 00:00:00 2001
From: Jens Axboe <[email protected]>
Date: Tue, 29 Sep 2026 06:52:17 -0600
Subject: [PATCH] io_uring: fix task_work add use-after-free with SQPOLL
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

For SQPOLL, the sqpoll thread runs task_work off its own list and doesn't need to be told about it, so it can pop and complete a request as soon as mpscq_push() has published it. If that was the last request holding the ring alive, io_ring_exit_work() then frees the ctx, stops the thread, and with it the tctx, while io_req_normal_work_add() is still looking at both after the push:

  BUG: KASAN: slab-use-after-free in io_req_normal_work_add+0x439/0x510
  Read of size 4 at addr ff11000000ca0000 by task repro/55
  (...)
  BUG: KASAN: slab-use-after-free in queue_work_on+0x25/0x70
  Write of size 8 at addr ff11000000c3bd00 by task repro/55

Hold an RCU read lock across the add, like io_req_local_work_add() already does, and have io_ring_exit_work() wait for a grace period for SQPOLL rings as well before freeing the ctx.

index 2cb9b58d04dd..c2ce83c7c1f1 100644
@@ -2405,8 +2405,8 @@ static __cold void io_ring_exit_work(struct work_struct *work)
 	spin_lock(&ctx->completion_lock);
 	spin_unlock(&ctx->completion_lock);
 
-	/* pairs with RCU read section in io_req_local_work_add() */
-	if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
+	/* pairs with the RCU read sections in the task_work add paths */
+	if (ctx->flags & (IORING_SETUP_DEFER_TASKRUN | IORING_SETUP_SQPOLL))
 		synchronize_rcu();
 
 	io_ring_ctx_free(ctx);

index f573bcc3af6a..f9affd68dd26 100644
@@ -210,6 +210,9 @@ void io_req_normal_work_add(struct io_kiocb *req)
 	struct io_uring_task *tctx = req->tctx;
 	struct io_ring_ctx *ctx = req->ctx;
 
+	/* SQPOLL can retire the request on push, see io_ring_exit_work() */
+	guard(rcu)();
+
 	/* tw run already pending, nothing else to do */
 	if (!mpscq_push(&tctx->task_list, &req->io_task_work.node))
 		return;

From: Jens Axboe <[email protected]>

[ Upstream commit a92193c91e8839fe5fc209616ea95465ae4b919d ]

For SQPOLL, the sqpoll thread runs task_work off its own list and doesn't need to be told about it, so it can pop and complete a request as soon as mpscq_push() has published it. If that was the last request holding the ring alive, io_ring_exit_work() then frees the ctx, stops the thread, and with it the tctx, while io_req_normal_work_add() is still looking at both after the push:

  BUG: KASAN: slab-use-after-free in io_req_normal_work_add+0x439/0x510
  Read of size 4 at addr ff11000000ca0000 by task repro/55
  (...)
  BUG: KASAN: slab-use-after-free in queue_work_on+0x25/0x70
  Write of size 8 at addr ff11000000c3bd00 by task repro/55

Hold an RCU read lock across the add, like io_req_local_work_add() already does, and have io_ring_exit_work() wait for a grace period for SQPOLL rings as well before freeing the ctx.

---
 io_uring/io_uring.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

index fd64ba7a0927a..524669ee19982 100644
@@ -1341,6 +1341,9 @@ static void io_req_normal_work_add(struct io_kiocb *req)
 	struct io_uring_task *tctx = req->tctx;
 	struct io_ring_ctx *ctx = req->ctx;
 
+	/* SQPOLL can retire the request on push, see io_ring_exit_work() */
+	guard(rcu)();
+
 	/* task_work already pending, we're done */
 	if (!llist_add(&req->io_task_work.node, &tctx->task_list))
 		return;

@@ -3146,8 +3149,8 @@ static __cold void io_ring_exit_work(struct work_struct *work)
 	spin_lock(&ctx->completion_lock);
 	spin_unlock(&ctx->completion_lock);
 
-	/* pairs with RCU read section in io_req_local_work_add() */
-	if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
+	/* pairs with the RCU read sections in the task_work add paths */
+	if (ctx->flags & (IORING_SETUP_DEFER_TASKRUN | IORING_SETUP_SQPOLL))
 		synchronize_rcu();
 
 	io_ring_ctx_free(ctx);

2.53.0