Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull userns hardlink capability check fix from Eric Biederman:
 "This round just contains a single patch.  There has been a lot of
  other work this period but it is not quite ready yet, so I am pushing
  it until 4.5.

  The remaining change by Dirk Steinmetz wich fixes both Gentoo and
  Ubuntu containers allows hardlinks if we have the appropriate
  capabilities in the user namespace.  Security wise it is really a
  gimme as the user namespace root can already call setuid become that
  user and create the hardlink"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  namei: permit linking with CAP_FOWNER in userns

fs/namei.c

@@ -955,26 +955,23 @@ static bool safe_hardlink_source(struct inode *inode)
  *  - sysctl_protected_hardlinks enabled
  *  - fsuid does not match inode
  *  - hardlink source is unsafe (see safe_hardlink_source() above)
- *  - not CAP_FOWNER
+ *  - not CAP_FOWNER in a namespace with the inode owner uid mapped
  *
  * Returns 0 if successful, -ve on error.
  */
 static int may_linkat(struct path *link)
 {
-	const struct cred *cred;
 	struct inode *inode;
 
 	if (!sysctl_protected_hardlinks)
 		return 0;
 
-	cred = current_cred();
 	inode = link->dentry->d_inode;
 
 	/* Source inode owner (or CAP_FOWNER) can hardlink all they like,
 	 * otherwise, it must be a safe source.
 	 */
-	if (uid_eq(cred->fsuid, inode->i_uid) || safe_hardlink_source(inode) ||
-	    capable(CAP_FOWNER))
+	if (inode_owner_or_capable(inode) || safe_hardlink_source(inode))
 		return 0;
 
 	audit_log_link_denied("linkat", link);