Cache user_ns in struct cred

If !CONFIG_USERNS, have current_user_ns() defined to (&init_user_ns).

Get rid of _current_user_ns.  This requires nsown_capable() to be
defined in capability.c rather than as static inline in capability.h,
so do that.

Request_key needs init_user_ns defined at current_user_ns if
!CONFIG_USERNS, so forward-declare that in cred.h if !CONFIG_USERNS
at current_user_ns() define.

Compile-tested with and without CONFIG_USERNS.

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
[ This makes a huge performance difference for acl_permission_check(),
  up to 30%.  And that is one of the hottest kernel functions for loads
  that are pathname-lookup heavy.  ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 6 deletions

diff --git a/kernel/cred.c b/kernel/cred.c
index 5557b55048df..8093c16b84b1 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -54,6 +54,7 @@ struct cred init_cred = {
 	.cap_effective		= CAP_INIT_EFF_SET,
 	.cap_bset		= CAP_INIT_BSET,
 	.user			= INIT_USER,
+	.user_ns		= &init_user_ns,
 	.group_info		= &init_groups,
 #ifdef CONFIG_KEYS
 	.tgcred			= &init_tgcred,
@@ -410,6 +411,11 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 			goto error_put;
 	}
 
+	/* cache user_ns in cred.  Doesn't need a refcount because it will
+	 * stay pinned by cred->user
+	 */
+	new->user_ns = new->user->user_ns;
+
 #ifdef CONFIG_KEYS
 	/* new threads get their own thread keyrings if their parent already
 	 * had one */
@@ -741,12 +747,6 @@ int set_create_files_as(struct cred *new, struct inode *inode)
 }
 EXPORT_SYMBOL(set_create_files_as);
 
-struct user_namespace *current_user_ns(void)
-{
-	return _current_user_ns();
-}
-EXPORT_SYMBOL(current_user_ns);
-
 #ifdef CONFIG_DEBUG_CREDENTIALS
 
 bool creds_are_invalid(const struct cred *cred)