[PATCH 0/6] Constant Time Memory Comparisons Are Important

Whenever you're comparing two MACs, it's important to do this using
crypto_memneq instead of memcmp. With memcmp, you leak timing information,
which could then be used to iteratively forge a MAC. This is far too basic
of a mistake for us to have so pervasively in the year 2017, so let's begin
cleaning this stuff up. The following 6 locations were found with some
simple regex greps, but I'm sure more lurk below the surface. If you
maintain some code or know somebody who maintains some code that deals
with MACs, tell them to double check which comparison function they're
using.

Jason A. Donenfeld (6):
  sunrpc: use constant time memory comparison for mac
  net/ipv6: use constant time memory comparison for mac
  ccree: use constant time memory comparison for macs and tags
  security/keys: use constant time memory comparison for macs
  bluetooth/smp: use constant time memory comparison for secret values
  mac80211/wpa: use constant time memory comparison for MACs

Cc: Anna Schumaker <redacted>
Cc: David Howells <dhowells@redhat.com>
Cc: David Safford <redacted>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Gustavo Padovan <redacted>
Cc: "J. Bruce Fields" <redacted>
Cc: Jeff Layton <redacted>
Cc: Johan Hedberg <redacted>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Mimi Zohar <redacted>
Cc: Trond Myklebust <redacted>
Cc: keyrings@vger.kernel.org
Cc: linux-bluetooth@vger.kernel.org
Cc: linux-nfs@vger.kernel.org
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org

 drivers/staging/ccree/ssi_fips_ll.c   | 17 ++++++++-------
 net/bluetooth/smp.c                   | 39 ++++++++++++++++++-----------------
 net/ipv6/seg6_hmac.c                  |  3 ++-
 net/mac80211/wpa.c                    |  9 ++++----
 net/sunrpc/auth_gss/gss_krb5_crypto.c |  3 ++-
 security/keys/trusted.c               |  7 ++++---
 6 files changed, 42 insertions(+), 36 deletions(-)

-- 
2.13.1

Otherwise, we enable a MAC forgery via timing attack.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Cc: stable@vger.kernel.org
---
 net/ipv6/seg6_hmac.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/seg6_hmac.c b/net/ipv6/seg6_hmac.c
index f950cb53d5e3..54213c83b44e 100644
--- a/net/ipv6/seg6_hmac.c
+++ b/net/ipv6/seg6_hmac.c

@@ -38,6 +38,7 @@
 #include <net/xfrm.h>
 
 #include <linux/cryptohash.h>
+#include <crypto/algapi.h>
 #include <crypto/hash.h>
 #include <crypto/sha.h>
 #include <net/seg6.h>

@@ -274,7 +275,7 @@ bool seg6_hmac_validate_skb(struct sk_buff *skb)
 	if (seg6_hmac_compute(hinfo, srh, &ipv6_hdr(skb)->saddr, hmac_output))
 		return false;
 
-	if (memcmp(hmac_output, tlv->hmac, SEG6_HMAC_FIELD_LEN) != 0)
+	if (crypto_memneq(hmac_output, tlv->hmac, SEG6_HMAC_FIELD_LEN))
 		return false;
 
 	return true;

-- 
2.13.1

Am Samstag, 10. Juni 2017, 04:59:06 CEST schrieb Jason A. Donenfeld:

Hi Jason,

Whenever you're comparing two MACs, it's important to do this using
crypto_memneq instead of memcmp. With memcmp, you leak timing information,
which could then be used to iteratively forge a MAC. This is far too basic
of a mistake for us to have so pervasively in the year 2017, so let's begin
cleaning this stuff up. The following 6 locations were found with some
simple regex greps, but I'm sure more lurk below the surface. If you
maintain some code or know somebody who maintains some code that deals
with MACs, tell them to double check which comparison function they're
using.

Are you planning to send an update to your patch set? If yes, there is another 
one which should be converted too: crypto/rsa-pkcs1pad.c.

Otherwise, I will send a patch converting this one.

Thanks.

Ciao
Stephan
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Hi Stephan,

On Sun, Jun 11, 2017 at 11:06 PM, Stephan Müller [off-list ref] wrote:

Are you planning to send an update to your patch set? If yes, there is another
one which should be converted too: crypto/rsa-pkcs1pad.c.

I just sent an update to this thread patching that, per your
suggestion. Since these issues are expected to be cherry picked by
their respective committer, I figure we can just pile on the patches
here, listing the 0/6 intro email as each patch's parent.

Jason