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[RESEND,v2,07/18] fs: Check for invalid i_uid in may_follow_link()

Message ID 1451930639-94331-8-git-send-email-seth.forshee@canonical.com (mailing list archive)
State Superseded
Headers show

Commit Message

Seth Forshee Jan. 4, 2016, 6:03 p.m. UTC
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.

Add a new helper function, uid_valid_eq(), and use this to
validate that the ids in may_follow_link() are both equal and
valid. Also add an equivalent helper for gids, which is
currently unused.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
 fs/namei.c             |  2 +-
 include/linux/uidgid.h | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)
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diff --git a/fs/namei.c b/fs/namei.c
index 288e8a74bf88..4ccafd391697 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -902,7 +902,7 @@  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))
+	if (uid_valid_eq(parent->i_uid, inode->i_uid))
 		return 0;
 	if (nd->flags & LOOKUP_RCU)
diff --git a/include/linux/uidgid.h b/include/linux/uidgid.h
index 03835522dfcb..e09529fe2668 100644
--- a/include/linux/uidgid.h
+++ b/include/linux/uidgid.h
@@ -117,6 +117,16 @@  static inline bool gid_valid(kgid_t gid)
 	return __kgid_val(gid) != (gid_t) -1;
+static inline bool uid_valid_eq(kuid_t left, kuid_t right)
+	return uid_eq(left, right) && uid_valid(left);
+static inline bool gid_valid_eq(kgid_t left, kgid_t right)
+	return gid_eq(left, right) && gid_valid(left);
 extern kuid_t make_kuid(struct user_namespace *from, uid_t uid);