From: Li Nan linan122@huawei.com
[ Upstream commit c2da049f419417808466c529999170f5c3ef7d3d ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/nbd.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index daaf8805e876c..3f03cb3dc33cc 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -397,8 +397,16 @@ static u32 req_to_nbd_cmd_type(struct request *req)
static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd) { - if (refcount_inc_not_zero(&nbd->config_refs)) + if (refcount_inc_not_zero(&nbd->config_refs)) { + /* + * Add smp_mb__after_atomic to ensure that reading nbd->config_refs + * and reading nbd->config is ordered. The pair is the barrier in + * nbd_alloc_and_init_config(), avoid nbd->config_refs is set + * before nbd->config. + */ + smp_mb__after_atomic(); return nbd->config; + }
return NULL; } @@ -1559,7 +1567,15 @@ static int nbd_alloc_and_init_config(struct nbd_device *nbd) init_waitqueue_head(&config->conn_wait); config->blksize_bits = NBD_DEF_BLKSIZE_BITS; atomic_set(&config->live_connections, 0); + nbd->config = config; + /* + * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment, + * its pair is the barrier in nbd_get_config_unlocked(). + * So nbd_get_config_unlocked() won't see nbd->config as null after + * refcount_inc_not_zero() succeed. + */ + smp_mb__before_atomic(); refcount_set(&nbd->config_refs, 1);
return 0;