aboutsummaryrefslogtreecommitdiffstats
path: root/main/hostapd/0004-SAE-Avoid-branches-in-is_quadratic_residue_blind.patch
diff options
context:
space:
mode:
Diffstat (limited to 'main/hostapd/0004-SAE-Avoid-branches-in-is_quadratic_residue_blind.patch')
-rw-r--r--main/hostapd/0004-SAE-Avoid-branches-in-is_quadratic_residue_blind.patch144
1 files changed, 144 insertions, 0 deletions
diff --git a/main/hostapd/0004-SAE-Avoid-branches-in-is_quadratic_residue_blind.patch b/main/hostapd/0004-SAE-Avoid-branches-in-is_quadratic_residue_blind.patch
new file mode 100644
index 0000000000..aad9b1d4a4
--- /dev/null
+++ b/main/hostapd/0004-SAE-Avoid-branches-in-is_quadratic_residue_blind.patch
@@ -0,0 +1,144 @@
+From 362704dda04507e7ebb8035122e83d9f0ae7c320 Mon Sep 17 00:00:00 2001
+From: Jouni Malinen <jouni@codeaurora.org>
+Date: Tue, 26 Feb 2019 19:34:38 +0200
+Subject: [PATCH] SAE: Avoid branches in is_quadratic_residue_blind()
+
+Make the non-failure path in the function proceed without branches based
+on r_odd and in constant time to minimize risk of observable differences
+in timing or cache use. (CVE-2019-9494)
+
+Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
+---
+ src/common/sae.c | 64 ++++++++++++++++++++++++++++--------------------
+ 1 file changed, 37 insertions(+), 27 deletions(-)
+
+diff --git a/src/common/sae.c b/src/common/sae.c
+index d55323bcd..5df9b95aa 100644
+--- a/src/common/sae.c
++++ b/src/common/sae.c
+@@ -232,12 +232,14 @@ get_rand_1_to_p_1(const u8 *prime, size_t prime_len, size_t prime_bits,
+
+ static int is_quadratic_residue_blind(struct sae_data *sae,
+ const u8 *prime, size_t bits,
+- const struct crypto_bignum *qr,
+- const struct crypto_bignum *qnr,
++ const u8 *qr, const u8 *qnr,
+ const struct crypto_bignum *y_sqr)
+ {
+- struct crypto_bignum *r, *num;
++ struct crypto_bignum *r, *num, *qr_or_qnr = NULL;
+ int r_odd, check, res = -1;
++ u8 qr_or_qnr_bin[SAE_MAX_ECC_PRIME_LEN];
++ size_t prime_len = sae->tmp->prime_len;
++ unsigned int mask;
+
+ /*
+ * Use the blinding technique to mask y_sqr while determining
+@@ -248,7 +250,7 @@ static int is_quadratic_residue_blind(struct sae_data *sae,
+ * r = a random number between 1 and p-1, inclusive
+ * num = (v * r * r) modulo p
+ */
+- r = get_rand_1_to_p_1(prime, sae->tmp->prime_len, bits, &r_odd);
++ r = get_rand_1_to_p_1(prime, prime_len, bits, &r_odd);
+ if (!r)
+ return -1;
+
+@@ -258,41 +260,45 @@ static int is_quadratic_residue_blind(struct sae_data *sae,
+ crypto_bignum_mulmod(num, r, sae->tmp->prime, num) < 0)
+ goto fail;
+
+- if (r_odd) {
+- /*
+- * num = (num * qr) module p
+- * LGR(num, p) = 1 ==> quadratic residue
+- */
+- if (crypto_bignum_mulmod(num, qr, sae->tmp->prime, num) < 0)
+- goto fail;
+- check = 1;
+- } else {
+- /*
+- * num = (num * qnr) module p
+- * LGR(num, p) = -1 ==> quadratic residue
+- */
+- if (crypto_bignum_mulmod(num, qnr, sae->tmp->prime, num) < 0)
+- goto fail;
+- check = -1;
+- }
++ /*
++ * Need to minimize differences in handling different cases, so try to
++ * avoid branches and timing differences.
++ *
++ * If r_odd:
++ * num = (num * qr) module p
++ * LGR(num, p) = 1 ==> quadratic residue
++ * else:
++ * num = (num * qnr) module p
++ * LGR(num, p) = -1 ==> quadratic residue
++ */
++ mask = const_time_is_zero(r_odd);
++ const_time_select_bin(mask, qnr, qr, prime_len, qr_or_qnr_bin);
++ qr_or_qnr = crypto_bignum_init_set(qr_or_qnr_bin, prime_len);
++ if (!qr_or_qnr ||
++ crypto_bignum_mulmod(num, qr_or_qnr, sae->tmp->prime, num) < 0)
++ goto fail;
++ /* r_odd is 0 or 1; branchless version of check = r_odd ? 1 : -1, */
++ check = const_time_select_int(mask, -1, 1);
+
+ res = crypto_bignum_legendre(num, sae->tmp->prime);
+ if (res == -2) {
+ res = -1;
+ goto fail;
+ }
+- res = res == check;
++ /* branchless version of res = res == check
++ * (res is -1, 0, or 1; check is -1 or 1) */
++ mask = const_time_eq(res, check);
++ res = const_time_select_int(mask, 1, 0);
+ fail:
+ crypto_bignum_deinit(num, 1);
+ crypto_bignum_deinit(r, 1);
++ crypto_bignum_deinit(qr_or_qnr, 1);
+ return res;
+ }
+
+
+ static int sae_test_pwd_seed_ecc(struct sae_data *sae, const u8 *pwd_seed,
+- const u8 *prime,
+- const struct crypto_bignum *qr,
+- const struct crypto_bignum *qnr,
++ const u8 *prime, const u8 *qr, const u8 *qnr,
+ u8 *pwd_value)
+ {
+ struct crypto_bignum *y_sqr, *x_cand;
+@@ -452,6 +458,8 @@ static int sae_derive_pwe_ecc(struct sae_data *sae, const u8 *addr1,
+ struct crypto_bignum *x = NULL, *qr = NULL, *qnr = NULL;
+ u8 x_bin[SAE_MAX_ECC_PRIME_LEN];
+ u8 x_cand_bin[SAE_MAX_ECC_PRIME_LEN];
++ u8 qr_bin[SAE_MAX_ECC_PRIME_LEN];
++ u8 qnr_bin[SAE_MAX_ECC_PRIME_LEN];
+ size_t bits;
+ int res = -1;
+ u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_*
+@@ -476,7 +484,9 @@ static int sae_derive_pwe_ecc(struct sae_data *sae, const u8 *addr1,
+ * (qnr) modulo p for blinding purposes during the loop.
+ */
+ if (get_random_qr_qnr(prime, prime_len, sae->tmp->prime, bits,
+- &qr, &qnr) < 0)
++ &qr, &qnr) < 0 ||
++ crypto_bignum_to_bin(qr, qr_bin, sizeof(qr_bin), prime_len) < 0 ||
++ crypto_bignum_to_bin(qnr, qnr_bin, sizeof(qnr_bin), prime_len) < 0)
+ goto fail;
+
+ wpa_hexdump_ascii_key(MSG_DEBUG, "SAE: password",
+@@ -527,7 +537,7 @@ static int sae_derive_pwe_ecc(struct sae_data *sae, const u8 *addr1,
+ break;
+
+ res = sae_test_pwd_seed_ecc(sae, pwd_seed,
+- prime, qr, qnr, x_cand_bin);
++ prime, qr_bin, qnr_bin, x_cand_bin);
+ const_time_select_bin(found, x_bin, x_cand_bin, prime_len,
+ x_bin);
+ pwd_seed_odd = const_time_select_u8(
+--
+2.21.0
+