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Fri, 14 Mar 2025 12:14:35 -0700 (PDT) From: Joanne Koong To: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org Cc: bernd.schubert@fastmail.fm, kernel-team@meta.com Subject: [PATCH] fuse: fix uring race condition for null dereference of fc Date: Fri, 14 Mar 2025 12:13:34 -0700 Message-ID: <20250314191334.215741-1-joannelkoong@gmail.com> X-Mailer: git-send-email 2.47.1 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 There is a race condition leading to a kernel crash from a null dereference when attemping to access fc->lock in fuse_uring_create_queue(). fc may be NULL in the case where another thread is creating the uring in fuse_uring_create() and has set fc->ring but has not yet set ring->fc when fuse_uring_create_queue() reads ring->fc. This fix sets fc->ring only after ring->fc has been set, which guarantees now that ring->fc is a proper pointer when any queues are created. Signed-off-by: Joanne Koong Fixes: 24fe962c86f5 ("fuse: {io-uring} Handle SQEs - register commands") --- fs/fuse/dev_uring.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c index ab8c26042aa8..618a413ef400 100644 --- a/fs/fuse/dev_uring.c +++ b/fs/fuse/dev_uring.c @@ -235,9 +235,9 @@ static struct fuse_ring *fuse_uring_create(struct fuse_conn *fc) init_waitqueue_head(&ring->stop_waitq); - fc->ring = ring; ring->nr_queues = nr_queues; ring->fc = fc; + fc->ring = ring; ring->max_payload_sz = max_payload_size; atomic_set(&ring->queue_refs, 0);