nbd: fix null-ptr-dereference while accessing 'nbd->config'
Memory reordering may occur in nbd_genl_connect(), causing config_refs
to be set to 1 while nbd->config is still empty. Opening nbd at this
time will cause null-ptr-dereference.
T1 T2
nbd_open
nbd_get_config_unlocked
nbd_genl_connect
nbd_alloc_and_init_config
//memory reordered
refcount_set(&nbd->config_refs, 1) // 2
nbd->config
->null point
nbd->config = config // 1
Fix it by adding smp barrier to guarantee the execution sequence.
Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20231116162316.1740402-4-linan666@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>