[Devel,rh7,05/11] ms/fs: Check for invalid i_uid in may_follow_link()

Submitted by Konstantin Khorenko on June 22, 2017, 2:47 p.m.


Message ID 1498142878-2222-6-git-send-email-khorenko@virtuozzo.com
State New
Series "Revert "ms/cred: Reject inodes with invalid ids in set_create_file_as()""
Headers show

Commit Message

Konstantin Khorenko June 22, 2017, 2:47 p.m.
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>
(cherry picked from commit 2d7f9e2ad35e4e7a3086231f19bfab33c6a8a64a)


Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
 fs/namei.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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diff --git a/fs/namei.c b/fs/namei.c
index ede7535..1ee459f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -803,6 +803,7 @@  static inline int may_follow_link(struct path *link, struct nameidata *nd)
 	const struct inode *inode;
 	const struct inode *parent;
+	kuid_t puid;
 	if (!sysctl_protected_symlinks)
 		return 0;
@@ -818,7 +819,8 @@  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))
+	puid = parent->i_uid;
+	if (uid_valid(puid) && uid_eq(puid, inode->i_uid))
 		return 0;
 	audit_log_link_denied("follow_link", link);