CRED: Wrap task credential accesses in the UBIFS filesystem

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Artem Bityutskiy <dedekind@infradead.org>
Cc: Adrian Hunter <ext-adrian.hunter@nokia.com>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: James Morris <jmorris@namei.org>

fs/ubifs/budget.c

@@ -363,7 +363,7 @@ long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
  */
 static int can_use_rp(struct ubifs_info *c)
 {
-	if (current->fsuid == c->rp_uid || capable(CAP_SYS_RESOURCE) ||
+	if (current_fsuid() == c->rp_uid || capable(CAP_SYS_RESOURCE) ||
 	    (c->rp_gid != 0 && in_group_p(c->rp_gid)))
 		return 1;
 	return 0;

fs/ubifs/dir.c

@@ -104,13 +104,13 @@ struct inode *ubifs_new_inode(struct ubifs_info *c, const struct inode *dir,
 	 */
 	inode->i_flags |= (S_NOCMTIME);
 
-	inode->i_uid = current->fsuid;
+	inode->i_uid = current_fsuid();
 	if (dir->i_mode & S_ISGID) {
 		inode->i_gid = dir->i_gid;
 		if (S_ISDIR(mode))
 			mode |= S_ISGID;
 	} else
-		inode->i_gid = current->fsgid;
+		inode->i_gid = current_fsgid();
 	inode->i_mode = mode;
 	inode->i_mtime = inode->i_atime = inode->i_ctime =
 			 ubifs_current_time(inode);