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From f8f20717f87eff1f025f48ed585c7684debacf72 Mon Sep 17 00:00:00 2001
From: Jouni Malinen <jouni@codeaurora.org>
Date: Sat, 2 Mar 2019 12:45:33 +0200
Subject: [PATCH 08/14] SAE: Use const_time selection for PWE in FFC
This is an initial step towards making the FFC case use strictly
constant time operations similarly to the ECC case.
sae_test_pwd_seed_ffc() does not yet have constant time behavior,
though.
This is related to CVE-2019-9494.
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Upstream-Status: Backport
CVE: CVE-2019-9494
---
src/common/sae.c | 53 +++++++++++++++++++++++++++++++++++------------------
1 file changed, 35 insertions(+), 18 deletions(-)
diff --git a/src/common/sae.c b/src/common/sae.c
index 75b1b4a..fa9a145 100644
--- a/src/common/sae.c
+++ b/src/common/sae.c
@@ -612,17 +612,28 @@ static int sae_derive_pwe_ffc(struct sae_data *sae, const u8 *addr1,
const u8 *addr2, const u8 *password,
size_t password_len, const char *identifier)
{
- u8 counter, k;
+ u8 counter, k, sel_counter = 0;
u8 addrs[2 * ETH_ALEN];
const u8 *addr[3];
size_t len[3];
size_t num_elem;
- int found = 0;
- struct crypto_bignum *pwe = NULL;
+ u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_*
+ * mask */
+ u8 mask;
+ struct crypto_bignum *pwe;
+ size_t prime_len = sae->tmp->prime_len * 8;
+ u8 *pwe_buf;
crypto_bignum_deinit(sae->tmp->pwe_ffc, 1);
sae->tmp->pwe_ffc = NULL;
+ /* Allocate a buffer to maintain selected and candidate PWE for constant
+ * time selection. */
+ pwe_buf = os_zalloc(prime_len * 2);
+ pwe = crypto_bignum_init();
+ if (!pwe_buf || !pwe)
+ goto fail;
+
wpa_hexdump_ascii_key(MSG_DEBUG, "SAE: password",
password, password_len);
@@ -661,27 +672,33 @@ static int sae_derive_pwe_ffc(struct sae_data *sae, const u8 *addr1,
if (hmac_sha256_vector(addrs, sizeof(addrs), num_elem,
addr, len, pwd_seed) < 0)
break;
- if (!pwe) {
- pwe = crypto_bignum_init();
- if (!pwe)
- break;
- }
res = sae_test_pwd_seed_ffc(sae, pwd_seed, pwe);
+ /* res is -1 for fatal failure, 0 if a valid PWE was not found,
+ * or 1 if a valid PWE was found. */
if (res < 0)
break;
- if (res > 0) {
- found = 1;
- if (!sae->tmp->pwe_ffc) {
- wpa_printf(MSG_DEBUG, "SAE: Use this PWE");
- sae->tmp->pwe_ffc = pwe;
- pwe = NULL;
- }
- }
+ /* Store the candidate PWE into the second half of pwe_buf and
+ * the selected PWE in the beginning of pwe_buf using constant
+ * time selection. */
+ if (crypto_bignum_to_bin(pwe, pwe_buf + prime_len, prime_len,
+ prime_len) < 0)
+ break;
+ const_time_select_bin(found, pwe_buf, pwe_buf + prime_len,
+ prime_len, pwe_buf);
+ sel_counter = const_time_select_u8(found, sel_counter, counter);
+ mask = const_time_eq_u8(res, 1);
+ found = const_time_select_u8(found, found, mask);
}
- crypto_bignum_deinit(pwe, 1);
+ if (!found)
+ goto fail;
- return found ? 0 : -1;
+ wpa_printf(MSG_DEBUG, "SAE: Use PWE from counter = %02u", sel_counter);
+ sae->tmp->pwe_ffc = crypto_bignum_init_set(pwe_buf, prime_len);
+fail:
+ crypto_bignum_deinit(pwe, 1);
+ bin_clear_free(pwe_buf, prime_len * 2);
+ return sae->tmp->pwe_ffc ? 0 : -1;
}
--
2.7.4
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