linux-kernel - [PATCH v6 3/6] io_uring: ensure submitter_task is valid for io_ring

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Message-ID: <20251218024459.1083572-4-csander@purestorage.com>
Date: Wed, 17 Dec 2025 19:44:56 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: Jens Axboe <axboe@...nel.dk>,
	io-uring@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Joanne Koong <joannelkoong@...il.com>,
	Caleb Sander Mateos <csander@...estorage.com>,
	kernel test robot <oliver.sang@...el.com>,
	syzbot@...kaller.appspotmail.com
Subject: [PATCH v6 3/6] io_uring: ensure submitter_task is valid for io_ring_ctx's lifetime

If io_uring_create() fails after allocating the struct io_ring_ctx, it
may call io_ring_ctx_wait_and_kill() before submitter_task has been
assigned. This is currently harmless, as the submit and register paths
that check submitter_task aren't reachable until the io_ring_ctx has
been successfully created. However, a subsequent commit will expect
submitter_task to be set for every IORING_SETUP_SINGLE_ISSUER &&
!IORING_SETUP_R_DISABLED ctx. So assign ctx->submitter_task immediately
after allocating the ctx in io_uring_create().
Similarly, the reference on submitter_task is currently released early
in io_ring_ctx_free(). But it will soon be needed to acquire the uring
lock during the later call to io_req_caches_free(). So release the
submitter_task reference as the last thing before freeing the ctx.

Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202512101405.a7a2bdb2-lkp@intel.com
Tested-by: syzbot@...kaller.appspotmail.com
Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
---
 io_uring/io_uring.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 44ff5756b328..22086ac84278 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2852,12 +2852,10 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_destroy_buffers(ctx);
 	io_free_region(ctx->user, &ctx->param_region);
 	mutex_unlock(&ctx->uring_lock);
 	if (ctx->sq_creds)
 		put_cred(ctx->sq_creds);
-	if (ctx->submitter_task)
-		put_task_struct(ctx->submitter_task);
 
 	WARN_ON_ONCE(!list_empty(&ctx->ltimeout_list));
 
 	if (ctx->mm_account) {
 		mmdrop(ctx->mm_account);
@@ -2877,10 +2875,13 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	if (ctx->hash_map)
 		io_wq_put_hash(ctx->hash_map);
 	io_napi_free(ctx);
 	kvfree(ctx->cancel_table.hbs);
 	xa_destroy(&ctx->io_bl_xa);
+	/* Release submitter_task last, as any io_ring_ctx_lock() may use it */
+	if (ctx->submitter_task)
+		put_task_struct(ctx->submitter_task);
 	kfree(ctx);
 }
 
 static __cold void io_activate_pollwq_cb(struct callback_head *cb)
 {
@@ -3594,10 +3595,20 @@ static __cold int io_uring_create(struct io_ctx_config *config)
 
 	ctx = io_ring_ctx_alloc(p);
 	if (!ctx)
 		return -ENOMEM;
 
+	/* Assign submitter_task first, as any io_ring_ctx_lock() may use it */
+	if (ctx->flags & IORING_SETUP_SINGLE_ISSUER
+	    && !(ctx->flags & IORING_SETUP_R_DISABLED)) {
+		/*
+		 * Unlike io_register_enable_rings(), don't need WRITE_ONCE()
+		 * since ctx isn't yet accessible from other tasks
+		 */
+		ctx->submitter_task = get_task_struct(current);
+	}
+
 	ctx->clockid = CLOCK_MONOTONIC;
 	ctx->clock_offset = 0;
 
 	if (!(ctx->flags & IORING_SETUP_NO_SQARRAY))
 		static_branch_inc(&io_key_has_sqarray);
@@ -3662,19 +3673,10 @@ static __cold int io_uring_create(struct io_ctx_config *config)
 	if (copy_to_user(config->uptr, p, sizeof(*p))) {
 		ret = -EFAULT;
 		goto err;
 	}
 
-	if (ctx->flags & IORING_SETUP_SINGLE_ISSUER
-	    && !(ctx->flags & IORING_SETUP_R_DISABLED)) {
-		/*
-		 * Unlike io_register_enable_rings(), don't need WRITE_ONCE()
-		 * since ctx isn't yet accessible from other tasks
-		 */
-		ctx->submitter_task = get_task_struct(current);
-	}
-
 	file = io_uring_get_file(ctx);
 	if (IS_ERR(file)) {
 		ret = PTR_ERR(file);
 		goto err;
 	}
-- 
2.45.2