[PATCH] fuse: fix uring race condition for null dereference of fc

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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 <joannelkoong@xxxxxxxxx>
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);
 
-- 
2.47.1





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