linux-kernel - [PATCH v2 1/3] vfs: Check for invalid i_uid in may_follow

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Message-Id: <1409672696-15847-2-git-send-email-seth.forshee@canonical.com>
Date:	Tue,  2 Sep 2014 10:44:54 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Seth Forshee <seth.forshee@...onical.com>
Subject: [PATCH v2 1/3] vfs: Check for invalid i_uid in may_follow_link()

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. Prevent this
by adding a check that the uid is valid before the comparison.

Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
---
 fs/namei.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index a996bb48dfab..193da09e903e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -741,7 +741,7 @@ static inline int may_follow_link(struct path *link, struct nameidata *nd)
 		return 0;
 
 	/* Allowed if parent directory and link owner match. */
-	if (uid_eq(parent->i_uid, inode->i_uid))
+	if (uid_valid(inode->i_uid) && uid_eq(parent->i_uid, inode->i_uid))
 		return 0;
 
 	audit_log_link_denied("follow_link", link);
-- 
1.9.1

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