diff mbox

[review,04/12] fs: Check for invalid i_uid in may_follow_link()

Message ID 20160706181212.16267-4-ebiederm@xmission.com (mailing list archive)
State New, archived
Headers show

Commit Message

Eric W. Biederman July 6, 2016, 6:12 p.m. UTC 
From: Seth Forshee <seth.forshee@canonical.com>

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 <seth.forshee@canonical.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 fs/namei.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
diff mbox

Patch

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)