From: Jeremy Cline <jcline@redhat.com>
To: Theodore Ts'o <tytso@mit.edu>, Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
Jeremy Cline <jcline@redhat.com>,
stable@vger.kernel.org
Subject: [PATCH 3/3] ext4: mballoc: Fix spectre gadget in ext4_mb_simple_scan_group
Date: Fri, 27 Jul 2018 16:23:57 +0000 [thread overview]
Message-ID: <20180727162357.30801-4-jcline@redhat.com> (raw)
In-Reply-To: <20180727162357.30801-1-jcline@redhat.com>
'ac->ac_2order' is a user-controlled value used to index into
'grp->bb_counters' and based on the value at that index, 'ac->ac_found'
is written to. Clamp the value right after the bounds check to avoid a
speculative out-of-bounds read of 'grp->bb_counters'.
This also protects the access of the s_mb_offsets and s_mb_maxs arrays
inside mb_find_buddy().
These gadgets were discovered with the help of smatch:
* fs/ext4/mballoc.c:1896 ext4_mb_simple_scan_group() warn: potential
spectre issue 'grp->bb_counters' [w] (local cap)
* fs/ext4/mballoc.c:445 mb_find_buddy() warn: potential spectre issue
'EXT4_SB(e4b->bd_sb)->s_mb_offsets' [r] (local cap)
* fs/ext4/mballoc.c:446 mb_find_buddy() warn: potential spectre issue
'EXT4_SB(e4b->bd_sb)->s_mb_maxs' [r] (local cap)
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---
fs/ext4/mballoc.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index f7ab34088162..c0866007a949 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -14,6 +14,7 @@
#include <linux/log2.h>
#include <linux/module.h>
#include <linux/slab.h>
+#include <linux/nospec.h>
#include <linux/backing-dev.h>
#include <trace/events/ext4.h>
@@ -1893,6 +1894,7 @@ void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
BUG_ON(ac->ac_2order <= 0);
for (i = ac->ac_2order; i <= sb->s_blocksize_bits + 1; i++) {
+ i = array_index_nospec(i, sb->s_blocksize_bits + 2);
if (grp->bb_counters[i] == 0)
continue;
--
2.17.1
next prev parent reply other threads:[~2018-07-27 16:25 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-27 16:23 [PATCH 0/3] ext4: fix spectre v1 gadgets Jeremy Cline
2018-07-27 16:23 ` [PATCH 1/3] ext4: super: Fix spectre gadget in ext4_quota_on Jeremy Cline
2018-07-27 17:46 ` Josh Poimboeuf
2018-07-27 19:17 ` Jeremy Cline
2018-07-31 6:39 ` Andreas Dilger
2018-07-31 17:31 ` Josh Poimboeuf
2018-07-27 16:23 ` [PATCH 2/3] ext4: super: Fix spectre gadgets in ext4_quota_{read,write,off} Jeremy Cline
2018-07-27 16:23 ` Jeremy Cline [this message]
2018-07-27 18:10 ` [PATCH 3/3] ext4: mballoc: Fix spectre gadget in ext4_mb_simple_scan_group Josh Poimboeuf
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