# \[PATCH review 04/12\] fs: Check for invalid i\_uid in may\_follow\_link()

- From: Eric W. Biederman \<hidden\>
- Date: 2016-07-06 18:25:04 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/07/110457
- Thread: https://ratatoskr.run/linux-fsdevel/2016/07/110550/t.md

```text
From: Seth Forshee <redacted>

Filesystem uids which don't map into a user namespace may result
in inode->i_uid being INVALID_UID. A symlink and its parent
could have different owners in the filesystem can both get
mapped to INVALID_UID, which may result in following a symlink
when this would not have otherwise been permitted when protected
symlinks are enabled.

Signed-off-by: Seth Forshee <redacted>
Acked-by: Serge Hallyn <redacted>
Signed-off-by: Eric W. Biederman <redacted>
---
 fs/namei.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 757a32725d92..8701bd9a5270 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -901,6 +901,7 @@ static inline int may_follow_link(struct nameidata *nd)
 {
 	const struct inode *inode;
 	const struct inode *parent;
+	kuid_t puid;
 
 	if (!sysctl_protected_symlinks)
 		return 0;
@@ -916,7 +917,8 @@ static inline int may_follow_link(struct nameidata *nd)
 		return 0;
 
 	/* Allowed if parent directory and link owner match. */
-	if (uid_eq(parent->i_uid, inode->i_uid))
+	puid = parent->i_uid;
+	if (uid_valid(puid) && uid_eq(puid, inode->i_uid))
 		return 0;
 
 	if (nd->flags & LOOKUP_RCU)
-- 
2.8.3

```