[ 3.8.y.z extended stable ] Patch "dm verity: fix inability to use a few specific devices sizes" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    dm verity: fix inability to use a few specific devices sizes

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 961db4a18a9e92b3dcf3f3d637dd33b916dc55f8 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka at redhat.com>
Date: Wed, 10 Jul 2013 23:41:16 +0100
Subject: dm verity: fix inability to use a few specific devices sizes

commit b1bf2de07271932326af847a3c6a01fdfd29d4be upstream.

Fix a boundary condition that caused failure for certain device sizes.

The problem is reported at
  http://code.google.com/p/cryptsetup/issues/detail?id=160

For certain device sizes the number of hashes at a specific level was
calculated incorrectly.

It happens for example for a device with data and metadata block size 4096
that has 16385 blocks and algorithm sha256.

The user can test if he is affected by this bug by running the
"veritysetup verify" command and also by activating the dm-verity kernel
driver and reading the whole block device. If it passes without an error,
then the user is not affected.

The condition for the bug is:

Split the total number of data blocks (data_block_bits) into bit strings,
each string has hash_per_block_bits bits. hash_per_block_bits is
rounddown(log2(metadata_block_size/hash_digest_size)). Equivalently, you
can say that you convert data_blocks_bits to 2^hash_per_block_bits base.

If there some zero bit string below the most significant bit string and at
least one bit below this zero bit string is set, then the bug happens.

The same bug exists in the userspace veritysetup tool, so you must use
fixed veritysetup too if you want to use devices that are affected by
this boundary condition.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Cc: Milan Broz <gmazyland at gmail.com>
Signed-off-by: Alasdair G Kergon <agk at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm-verity.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index a746f1d..4112d90 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -831,9 +831,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	for (i = v->levels - 1; i >= 0; i--) {
 		sector_t s;
 		v->hash_level_block[i] = hash_position;
-		s = verity_position_at_level(v, v->data_blocks, i);
-		s = (s >> v->hash_per_block_bits) +
-		    !!(s & ((1 << v->hash_per_block_bits) - 1));
+		s = (v->data_blocks + ((sector_t)1 << ((i + 1) * v->hash_per_block_bits)) - 1)
+					>> ((i + 1) * v->hash_per_block_bits);
 		if (hash_position + s < hash_position) {
 			ti->error = "Hash device offset overflow";
 			r = -E2BIG;
--
1.8.1.2