mainline inclusion from mainline-v6.7-rc3 commit c2da049f419417808466c529999170f5c3ef7d3d category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8P7B3 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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> --- 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 5150cb651ae0..762ac42459da 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; -- 2.39.2