Hi Joanne, On 3/14/25 20:13, Joanne Koong wrote: > 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); > oh, I didn't get that and even KCSAN didn't complain. But I see that it would be possible. I'm just a bit scared that the compiler might re-order things on its own. What about this? diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c index 9d78c9f29a09..f33a7e6f5ec3 100644 --- a/fs/fuse/dev_uring.c +++ b/fs/fuse/dev_uring.c @@ -241,11 +241,12 @@ 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; ring->max_payload_sz = max_payload_size; atomic_set(&ring->queue_refs, 0); + /* Ensures initialization is visible before ring pointer */ + smp_store_release(&fc->ring, ring); spin_unlock(&fc->lock); return ring; Thanks, Bernd