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/fs/fs_context.c b/fs/fs_context.c
index 2834d1a..de1985e 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -80,6 +80,35 @@ static int vfs_parse_sb_flag(struct fs_context *fc, const char *key)
}
/**
+ * vfs_parse_fs_param_source - Handle setting "source" via parameter
+ * @fc: The filesystem context to modify
+ * @param: The parameter
+ *
+ * This is a simple helper for filesystems to verify that the "source" they
+ * accept is sane.
+ *
+ * Returns 0 on success, -ENOPARAM if this is not "source" parameter, and
+ * -EINVAL otherwise. In the event of failure, supplementary error information
+ * is logged.
+ */
+int vfs_parse_fs_param_source(struct fs_context *fc, struct fs_parameter *param)
+{
+ if (strcmp(param->key, "source") != 0)
+ return -ENOPARAM;
+
+ if (param->type != fs_value_is_string)
+ return invalf(fc, "Non-string source");
+
+ if (fc->source)
+ return invalf(fc, "Multiple sources");
+
+ fc->source = param->string;
+ param->string = NULL;
+ return 0;
+}
+EXPORT_SYMBOL(vfs_parse_fs_param_source);
+
+/**
* vfs_parse_fs_param - Add a single parameter to a superblock config
* @fc: The filesystem context to modify
* @param: The parameter
@@ -122,15 +151,9 @@ int vfs_parse_fs_param(struct fs_context *fc, struct fs_parameter *param)
/* If the filesystem doesn't take any arguments, give it the
* default handling of source.
*/
- if (strcmp(param->key, "source") == 0) {
- if (param->type != fs_value_is_string)
- return invalf(fc, "VFS: Non-string source");
- if (fc->source)
- return invalf(fc, "VFS: Multiple sources");
- fc->source = param->string;
- param->string = NULL;
- return 0;
- }
+ ret = vfs_parse_fs_param_source(fc, param);
+ if (ret != -ENOPARAM)
+ return ret;
return invalf(fc, "%s: Unknown parameter '%s'",
fc->fs_type->name, param->key);
@@ -504,16 +527,11 @@ static int legacy_parse_param(struct fs_context *fc, struct fs_parameter *param)
struct legacy_fs_context *ctx = fc->fs_private;
unsigned int size = ctx->data_size;
size_t len = 0;
+ int ret;
- if (strcmp(param->key, "source") == 0) {
- if (param->type != fs_value_is_string)
- return invalf(fc, "VFS: Legacy: Non-string source");
- if (fc->source)
- return invalf(fc, "VFS: Legacy: Multiple sources");
- fc->source = param->string;
- param->string = NULL;
- return 0;
- }
+ ret = vfs_parse_fs_param_source(fc, param);
+ if (ret != -ENOPARAM)
+ return ret;
if (ctx->param_type == LEGACY_FS_MONOLITHIC_PARAMS)
return invalf(fc, "VFS: Legacy: Can't mix monolithic and individual options");
