[PATCH 3.16 026/192] Bluetooth: use constant time memory comparison for secret values

Ben Hutchings
2017-10-09T13:20:05Z

From: "Jason A. Donenfeld" <Jason@zx2c4.com>

commit 329d82309824ff1082dc4a91a5bbed8c3bec1580 upstream.

This file is filled with complex cryptography. Thus, the comparisons of
MACs and secret keys and curve points and so forth should not add timing
attacks, which could either result in a direct forgery, or, given the
complexity, some other type of attack.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
[bwh: Backported to 3.16:
- Drop inapplicable changes
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -22,6 +22,7 @@

#include <linux/crypto.h>
#include <linux/scatterlist.h>
+#include <crypto/algapi.h>
#include <crypto/b128ops.h>

#include <net/bluetooth/bluetooth.h>
@@ -153,7 +154,7 @@ bool smp_irk_matches(struct crypto_blkci
if (err)
return false;

- return !memcmp(bdaddr->b, hash, 3);
+ return !crypto_memneq(bdaddr->b, hash, 3);
}

int smp_generate_rpa(struct crypto_blkcipher *tfm, u8 irk[16], bdaddr_t *rpa)
@@ -533,7 +534,7 @@ static u8 smp_random(struct smp_chan *sm
if (ret)
return SMP_UNSPECIFIED;

- if (memcmp(smp->pcnf, confirm, sizeof(smp->pcnf)) != 0) {
+ if (crypto_memneq(smp->pcnf, confirm, sizeof(smp->pcnf))) {
BT_ERR("Pairing failed (confirmation values mismatch)");
return SMP_CONFIRM_FAILED;
}