[PATCH] virtiofs: fix NULL dereference in virtio_fs_add_queues_sysfs()

[Qianchang Zhao <pioooooooooip@gmail.com>]

virtio_fs_add_queues_sysfs() creates per-queue sysfs kobjects via
kobject_create_and_add(). The current code checks the wrong variable
after the allocation:

- kobject_create_and_add() may return NULL on failure.
- The code incorrectly checks fs->mqs_kobj (the parent kobject), which is
  expected to be non-NULL at this point.
- If kobject_create_and_add() fails, fsvq->kobj is NULL but the code can
  still call sysfs_create_group(fsvq->kobj, ...), leading to a NULL pointer
  dereference and kernel panic (DoS).

Fix by validating fsvq->kobj immediately after kobject_create_and_add()
and aborting on failure, so sysfs_create_group() is never called with a
NULL kobject.

Reported-by: Qianchang Zhao <pioooooooooip@gmail.com>
Reported-by: Zhitong Liu <liuzhitong1993@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Qianchang Zhao <pioooooooooip@gmail.com>
---
 fs/fuse/virtio_fs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 6bc7c97b0..b2f6486fe 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -373,7 +373,7 @@ static int virtio_fs_add_queues_sysfs(struct virtio_fs *fs)
 
 		sprintf(buff, "%d", i);
 		fsvq->kobj = kobject_create_and_add(buff, fs->mqs_kobj);
-		if (!fs->mqs_kobj) {
+		if (!fsvq->kobj) {
 			ret = -ENOMEM;
 			goto out_del;
 		}
-- 
2.34.1