From: Eric Sandeen <sandeen@redhat.com>
Date: Tue, 28 Oct 2008 13:09:33 -0500
Subject: [fs] ext4: delay capable checks to avoid avc denials
Message-id: 4907555D.8050101@redhat.com
O-Subject: [PATCH RHEL5.3] ext4: delay capable() checks to avoid avc denials
Bugzilla: 467216
RH-Acked-by: Josef Bacik <jbacik@redhat.com>
RH-Acked-by: Eric Paris <eparis@redhat.com>

This is for Bug 467216 - avc: denied { sys_resource } when using ext4dev partitions

ext4_has_free_blocks() is called often, and it checks capable(CAP_SYS_RESOURCE)
each time, which is leading to these denials.

Per eparis' suggestion, we can just invert the logic so that capable()
is the last thing checked, and for most users, this won't trigger the denial:

> so selinux is only going to complain if you have the capability according
> to capabilities (aka you are root) but selinux doesn't give you the perm
> so non-root should silently fail the capable() check and root should pass
> the fsuid check

With the revised logic, we will first test (sbi->s_resuid == current->fsuid)
so the root user will not wind up in the capable() check.

A slightly different fix was sent upstream:
http://marc.info/?l=linux-ext4&m=122488084212789&w=2 <http://marc.info/?l=linux-ext4&m=122488084212789&w=2>
http://marc.info/?l=linux-ext4&m=122488090912882&w=2 <http://marc.info/?l=linux-ext4&m=122488090912882&w=2>

but the below is a bit safer for a last-minute RHEL change.

Note, "root blocks" indicates how many blocks should be factored in as
reserved when calculating available space.  Setting root_blocks = 0 means
that all space is available for use (i.e. when any of those tests are met).

Thanks,
-Eric

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index d158d13..1eeb5e0 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -1612,15 +1612,15 @@ out:
 ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi,
 						ext4_fsblk_t nblocks)
 {
-	ext4_fsblk_t free_blocks;
-	ext4_fsblk_t root_blocks = 0;
+	ext4_fsblk_t free_blocks, root_blocks;
 
 	free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
+	root_blocks = ext4_r_blocks_count(sbi->s_es);
 
-	if (!capable(CAP_SYS_RESOURCE) &&
-		sbi->s_resuid != current->fsuid &&
-		(sbi->s_resgid == 0 || !in_group_p(sbi->s_resgid)))
-		root_blocks = ext4_r_blocks_count(sbi->s_es);
+	if (sbi->s_resuid == current->fsuid ||
+	    ((sbi->s_resgid != 0) && in_group_p(sbi->s_resgid)) ||
+	    capable(CAP_SYS_RESOURCE))
+		root_blocks = 0;
 #ifdef CONFIG_SMP
 	if (free_blocks - root_blocks < FBC_BATCH)
 		free_blocks =