linux-ext4 - [PATCH] ext4: limit group search loop for non-extent files

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <5184230E.6020500@redhat.com>
Date:	Fri, 03 May 2013 15:50:22 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
CC:	Lachlan McIlroy <lmcilroy@...hat.com>
Subject: [PATCH] ext4: limit group search loop for non-extent files

From: Lachlan McIlroy <lmcilroy@...hat.com>

In the case where we are allocating for a non-extent file,
we must limit the groups we allocate from to those below
2^32 blocks, and ext4_mb_regular_allocator() attempts to
do this initially by putting a cap on ngroups for the
subsequent search loop.

However, the initial target group comes in from the 
allocation context (ac), and it may already be beyond
the artificially limited ngroups.  In this case,
the limit

	if (group == ngroups)
		group = 0;

at the top of the loop is never true, and the loop will
run away.

Catch this case inside the loop and reset the search to
start at group 0.

[sandeen@...hat.com: add commit msg & comments]

Signed-off-by: Eric Sandeen <sandeen@...hat.com>
---

p.s. I suppose this limit could go after the assignment
from ac->ac_g_ex.fe_group, depending on your sense
of style...

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index ee6614b..f54baee 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1994,7 +1994,11 @@ repeat:
 		group = ac->ac_g_ex.fe_group;

 		for (i = 0; i < ngroups; group++, i++) {
-			if (group == ngroups)
+			/*
+			 * Artificially restricted ngroups for non-extent
+			 * files makes group > ngroups possible on first loop.
+			 */
+			if (group >= ngroups)
 				group = 0;

 			/* This now checks without needing the buddy page */

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html