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| author | Li Nan <linan122@huawei.com> | 2023-11-16 17:23:16 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2023-11-20 18:16:44 +0100 |
| commit | c2da049f419417808466c529999170f5c3ef7d3d (patch) | |
| tree | 995e8ca613b5d08357091eeb6770ed9db542a6b9 /drivers/block | |
| parent | nbd: factor out a helper to get nbd_config without holding 'config_lock' (diff) | |
| download | linux-c2da049f419417808466c529999170f5c3ef7d3d.tar.xz linux-c2da049f419417808466c529999170f5c3ef7d3d.zip | |
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>
Diffstat (limited to 'drivers/block')
| -rw-r--r-- | drivers/block/nbd.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index daaf8805e876..3f03cb3dc33c 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; |