hostapd: SAE/EAP-pwd side-channel attack update

Fixes this security problem:
* SAE/EAP-pwd side-channel attack update
https://w1.fi/security/2019-6/sae-eap-pwd-side-channel-attack-update.txt

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 7bed9bf10fc8d05df34c7efc66e8b4ade37a1a0c)

1 files changed, 54 insertions, 0 deletions

diff --git a/package/network/services/hostapd/patches/066-0004-SAE-Run-through-prf-result-processing-even-if-it-pri.patch b/package/network/services/hostapd/patches/066-0004-SAE-Run-through-prf-result-processing-even-if-it-pri.patch
new file mode 100644
index 0000000000..7337cb35bd
--- /dev/null
+++ b/package/network/services/hostapd/patches/066-0004-SAE-Run-through-prf-result-processing-even-if-it-pri.patch
@@ -0,0 +1,54 @@
+From a25b48118d75f3c2d7cb1b2c3b4cffb13091a34c Mon Sep 17 00:00:00 2001
+From: Jouni Malinen <j@w1.fi>
+Date: Mon, 24 Jun 2019 23:01:06 +0300
+Subject: [PATCH 4/6] SAE: Run through prf result processing even if it >=
+ prime
+
+This reduces differences in timing and memory access within the
+hunting-and-pecking loop for ECC groups that have a prime that is not
+close to a power of two (e.g., Brainpool curves).
+
+Signed-off-by: Jouni Malinen <j@w1.fi>
+(cherry picked from commit 147bf7b88a9c231322b5b574263071ca6dbb0503)
+---
+ src/common/sae.c | 15 ++++++++++++---
+ 1 file changed, 12 insertions(+), 3 deletions(-)
+
+--- a/src/common/sae.c
++++ b/src/common/sae.c
+@@ -304,6 +304,8 @@ static int sae_test_pwd_seed_ecc(struct
+ 	struct crypto_bignum *y_sqr, *x_cand;
+ 	int res;
+ 	size_t bits;
++	int cmp_prime;
++	unsigned int in_range;
+ 
+ 	wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-seed", pwd_seed, SHA256_MAC_LEN);
+ 
+@@ -317,8 +319,13 @@ static int sae_test_pwd_seed_ecc(struct
+ 	wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-value",
+ 			pwd_value, sae->tmp->prime_len);
+ 
+-	if (const_time_memcmp(pwd_value, prime, sae->tmp->prime_len) >= 0)
+-		return 0;
++	cmp_prime = const_time_memcmp(pwd_value, prime, sae->tmp->prime_len);
++	/* Create a const_time mask for selection based on prf result
++	 * being smaller than prime. */
++	in_range = const_time_fill_msb((unsigned int) cmp_prime);
++	/* The algorithm description would skip the next steps if
++	 * cmp_prime >= 0 (reutnr 0 here), but go through them regardless to
++	 * minimize externally observable differences in behavior. */
+ 
+ 	x_cand = crypto_bignum_init_set(pwd_value, sae->tmp->prime_len);
+ 	if (!x_cand)
+@@ -330,7 +337,9 @@ static int sae_test_pwd_seed_ecc(struct
+ 
+ 	res = is_quadratic_residue_blind(sae, prime, bits, qr, qnr, y_sqr);
+ 	crypto_bignum_deinit(y_sqr, 1);
+-	return res;
++	if (res < 0)
++		return res;
++	return const_time_select_int(in_range, res, 0);
+ }
+ 
+