dm integrity: introduce the "fix_hmac" argument

The "fix_hmac" argument improves security of internal_hash and
journal_mac:
- the section number is mixed to the mac, so that an attacker can't
  copy sectors from one journal section to another journal section
- the superblock is protected by journal_mac
- a 16-byte salt stored in the superblock is mixed to the mac, so
  that the attacker can't detect that two disks have the same hmac
  key and also to disallow the attacker to move sectors from one
  disk to another

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reported-by: Daniel Glockner <dg@emlix.com>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com> # ReST fix
Tested-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/dm-integrity.rst b/Documentation/admin-guide/device-mapper/dm-integrity.rst
index 2cc5488acbd9..ef762857da95 100644
--- a/Documentation/admin-guide/device-mapper/dm-integrity.rst
+++ b/Documentation/admin-guide/device-mapper/dm-integrity.rst
@@ -186,6 +186,17 @@ fix_padding
 	space-efficient. If this option is not present, large padding is
 	used - that is for compatibility with older kernels.
 
+fix_hmac
+	Improve security of internal_hash and journal_mac:
+
+	- the section number is mixed to the mac, so that an attacker can't
+	  copy sectors from one journal section to another journal section
+	- the superblock is protected by journal_mac
+	- a 16-byte salt stored in the superblock is mixed to the mac, so
+	  that the attacker can't detect that two disks have the same hmac
+	  key and also to disallow the attacker to move sectors from one
+	  disk to another
+
 legacy_recalculate
 	Allow recalculating of volumes with HMAC keys. This is disabled by
 	default for security reasons - an attacker could modify the volume,