CRED: Wrap task credential accesses in the Ext2 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: linux-ext4@vger.kernel.org
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index 6dac7ba..4a29d63 100644
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -1193,7 +1193,7 @@
 	free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
 	root_blocks = le32_to_cpu(sbi->s_es->s_r_blocks_count);
 	if (free_blocks < root_blocks + 1 && !capable(CAP_SYS_RESOURCE) &&
-		sbi->s_resuid != current->fsuid &&
+		sbi->s_resuid != current_fsuid() &&
 		(sbi->s_resgid == 0 || !in_group_p (sbi->s_resgid))) {
 		return 0;
 	}