fs: add vfs_parse_fs_param_source() helper
Add a simple helper that filesystems can use in their parameter parser
to parse the "source" parameter. A few places open-coded this function
and that already caused a bug in the cgroup v1 parser that we fixed.
Let's make it harder to get this wrong by introducing a helper which
performs all necessary checks.
Link: https://syzkaller.appspot.com/bug?id=6312526aba5beae046fdae8f00399f87aab48b12
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 527917c..8d6bf56 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -911,15 +911,11 @@ int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
opt = fs_parse(fc, cgroup1_fs_parameters, param, &result);
if (opt == -ENOPARAM) {
- if (strcmp(param->key, "source") == 0) {
- if (param->type != fs_value_is_string)
- return invalf(fc, "Non-string source");
- if (fc->source)
- return invalf(fc, "Multiple sources not supported");
- fc->source = param->string;
- param->string = NULL;
- return 0;
- }
+ int ret;
+
+ ret = vfs_parse_fs_param_source(fc, param);
+ if (ret != -ENOPARAM)
+ return ret;
for_each_subsys(ss, i) {
if (strcmp(param->key, ss->legacy_name))
continue;