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

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

diff --combined fs/namei.c
index 33e9495a31293e2c080b5b0bd2e50523a460ceee,29fc6a657477cf49eaa4a722f2b2da39f6c387a6..0d3340b32e14bce04bcd28e5e6dc5fdbe3627c1a
--- 1/fs/namei.c
--- 2/fs/namei.c
+++ b/fs/namei.c
@@@ -955,26 -955,23 +955,23 @@@ static bool safe_hardlink_source(struc
   *  - 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);
@@@ -1558,6 -1555,8 +1555,6 @@@ static int lookup_fast(struct nameidat
                negative = d_is_negative(dentry);
                if (read_seqcount_retry(&dentry->d_seq, seq))
                        return -ECHILD;
 -              if (negative)
 -                      return -ENOENT;
  
                /*
                 * This sequence count validates that the parent had no
@@@ -1578,12 -1577,6 +1575,12 @@@
                                goto unlazy;
                        }
                }
 +              /*
 +               * Note: do negative dentry check after revalidation in
 +               * case that drops it.
 +               */
 +              if (negative)
 +                      return -ENOENT;
                path->mnt = mnt;
                path->dentry = dentry;
                if (likely(__follow_mount_rcu(nd, path, inode, seqp)))