virtiofs: add filesystem context source name check

In certain scenarios, for example, during fuzz testing, the source
name may be NULL, which could lead to a kernel panic. Therefore, an
extra check for the source name should be added.

Fixes: a62a8ef ("virtio-fs: add virtiofs filesystem")
Cc: <[email protected]> # all LTS kernels
Signed-off-by: Xiangsheng Hou <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: mtk-xiangsheng

fs/fuse/virtio_fs.c

@@ -1669,6 +1669,9 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
 	unsigned int virtqueue_size;
 	int err = -EIO;
 
+	if (!fsc->source)
+		return invalf(fsc, "No source specified");
+
 	/* This gets a reference on virtio_fs object. This ptr gets installed
 	 * in fc->iq->priv. Once fuse_conn is going away, it calls ->put()
 	 * to drop the reference to this object.