btrfs: add the missing error handling inside get_canonical_dev_path

Inside function get_canonical_dev_path(), we call d_path() to get the
final device path.

But d_path() can return error, and in that case the next strscpy() call
will trigger an invalid memory access.

Add back the missing error handling for d_path().

Reported-by: Boris Burkov <boris@bur.io>
Fixes: 7e06de7 ("btrfs: canonicalize the device path before adding it")
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -798,6 +798,10 @@ static int get_canonical_dev_path(const char *dev_path, char *canonical)
 	if (ret)
 		goto out;
 	resolved_path = d_path(&path, path_buf, PATH_MAX);
+	if (IS_ERR(resolved_path)) {
+		ret = PTR_ERR(resolved_path);
+		goto out;
+	}
 	ret = strscpy(canonical, resolved_path, PATH_MAX);
 out:
 	kfree(path_buf);