nettle: add security patch

Fixes:
CVE-2016-6489 - RSA code is vulnerable to cache sharing related attacks.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

2 files changed, 183 insertions, 0 deletions

diff --git a/package/nettle/0002-fix-CVE-2016-6489.patch b/package/nettle/0002-fix-CVE-2016-6489.patch
new file mode 100644
index 000000000..8c99ff72f
--- /dev/null
+++ b/package/nettle/0002-fix-CVE-2016-6489.patch
@@ -0,0 +1,181 @@
+From 6450224f3e3c78fdfa37eadbe6ada8301279f6c1 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
+Date: Mon, 20 Jun 2016 20:04:56 +0200
+Subject: Use mpz_powm_sec.
+Subject: Check for invalid keys, with even p, in dsa_sign.
+Subject: Reject invalid keys, with even moduli, in rsa_compute_root_tr.
+Subject: Reject invalid RSA keys with even modulo.
+
+Patch status: upstream
+
+Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
+
+diff --git a/bignum.h b/bignum.h
+index 24158e0..0d30534 100644
+--- a/bignum.h
++++ b/bignum.h
+@@ -53,6 +53,8 @@
+ # define mpz_combit mpz_combit
+ # define mpz_import mpz_import
+ # define mpz_export mpz_export
++/* Side-channel silent powm not available in mini-gmp. */
++# define mpz_powm_sec mpz_powm
+ #else
+ # include <gmp.h>
+ #endif
+diff --git a/configure.ac b/configure.ac
+index e1ee64c..1e88477 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -236,9 +236,9 @@ fi
+ # Checks for libraries
+ if test "x$enable_public_key" = "xyes" ; then
+   if test "x$enable_mini_gmp" = "xno" ; then
+-    AC_CHECK_LIB(gmp, __gmpz_getlimbn,,
++    AC_CHECK_LIB(gmp, __gmpz_powm_sec,,
+         [AC_MSG_WARN(
+-    [GNU MP not found, or not 3.1 or up, see http://gmplib.org/.
++    [GNU MP not found, or too old. GMP-5.0 or later is needed, see http://gmplib.org/.
+     Support for public key algorithms will be unavailable.])]
+         enable_public_key=no)
+ 
+diff --git a/dsa-sign.c b/dsa-sign.c
+index 62c7d4a..b713743 100644
+--- a/dsa-sign.c
++++ b/dsa-sign.c
+@@ -56,6 +56,11 @@ dsa_sign(const struct dsa_params *params,
+   mpz_t tmp;
+   int res;
+   
++  /* Check that p is odd, so that invalid keys don't result in a crash
++     inside mpz_powm_sec. */
++  if (mpz_even_p (params->p))
++    return 0;
++
+   /* Select k, 0<k<q, randomly */
+   mpz_init_set(tmp, params->q);
+   mpz_sub_ui(tmp, tmp, 1);
+@@ -65,7 +70,7 @@ dsa_sign(const struct dsa_params *params,
+   mpz_add_ui(k, k, 1);
+ 
+   /* Compute r = (g^k (mod p)) (mod q) */
+-  mpz_powm(tmp, params->g, k, params->p);
++  mpz_powm_sec(tmp, params->g, k, params->p);
+   mpz_fdiv_r(signature->r, tmp, params->q);
+ 
+   /* Compute hash */
+diff --git a/rsa-blind.c b/rsa-blind.c
+index 7662f50..16b03d7 100644
+--- a/rsa-blind.c
++++ b/rsa-blind.c
+@@ -61,7 +61,7 @@ _rsa_blind (const struct rsa_public_key *pub,
+   while (!mpz_invert (ri, r, pub->n));
+ 
+   /* c = c*(r^e) mod n */
+-  mpz_powm(r, r, pub->e, pub->n);
++  mpz_powm_sec(r, r, pub->e, pub->n);
+   mpz_mul(c, c, r);
+   mpz_fdiv_r(c, c, pub->n);
+ 
+diff --git a/rsa-sign-tr.c b/rsa-sign-tr.c
+index 3d80ed4..8542cae 100644
+--- a/rsa-sign-tr.c
++++ b/rsa-sign-tr.c
+@@ -60,7 +60,7 @@ rsa_blind (const struct rsa_public_key *pub,
+   while (!mpz_invert (ri, r, pub->n));
+ 
+   /* c = c*(r^e) mod n */
+-  mpz_powm(r, r, pub->e, pub->n);
++  mpz_powm_sec(r, r, pub->e, pub->n);
+   mpz_mul(c, m, r);
+   mpz_fdiv_r(c, c, pub->n);
+ 
+@@ -88,6 +88,14 @@ rsa_compute_root_tr(const struct rsa_public_key *pub,
+   int res;
+   mpz_t t, mb, xb, ri;
+ 
++  /* mpz_powm_sec handles only odd moduli. If p, q or n is even, the
++     key is invalid and rejected by rsa_private_key_prepare. However,
++     some applications, notably gnutls, don't use this function, and
++     we don't want an invalid key to lead to a crash down inside
++     mpz_powm_sec. So do an additional check here. */
++  if (mpz_even_p (pub->n) || mpz_even_p (key->p) || mpz_even_p (key->q))
++    return 0;
++
+   mpz_init (mb);
+   mpz_init (xb);
+   mpz_init (ri);
+@@ -97,7 +105,7 @@ rsa_compute_root_tr(const struct rsa_public_key *pub,
+ 
+   rsa_compute_root (key, xb, mb);
+ 
+-  mpz_powm(t, xb, pub->e, pub->n);
++  mpz_powm_sec(t, xb, pub->e, pub->n);
+   res = (mpz_cmp(mb, t) == 0);
+ 
+   if (res)
+diff --git a/rsa-sign.c b/rsa-sign.c
+index eba7388..4832352 100644
+--- a/rsa-sign.c
++++ b/rsa-sign.c
+@@ -96,11 +96,11 @@ rsa_compute_root(const struct rsa_private_key *key,
+ 
+   /* Compute xq = m^d % q = (m%q)^b % q */
+   mpz_fdiv_r(xq, m, key->q);
+-  mpz_powm(xq, xq, key->b, key->q);
++  mpz_powm_sec(xq, xq, key->b, key->q);
+ 
+   /* Compute xp = m^d % p = (m%p)^a % p */
+   mpz_fdiv_r(xp, m, key->p);
+-  mpz_powm(xp, xp, key->a, key->p);
++  mpz_powm_sec(xp, xp, key->a, key->p);
+ 
+   /* Set xp' = (xp - xq) c % p. */
+   mpz_sub(xp, xp, xq);
+diff --git a/rsa.c b/rsa.c
+index 19d93de..f594140 100644
+--- a/rsa.c
++++ b/rsa.c
+@@ -58,13 +58,18 @@ rsa_public_key_clear(struct rsa_public_key *key)
+ }
+ 
+ /* Computes the size, in octets, of a the modulo. Returns 0 if the
+- * modulo is too small to be useful. */
+-
++ * modulo is too small to be useful, or otherwise appears invalid. */
+ size_t
+ _rsa_check_size(mpz_t n)
+ {
+   /* Round upwards */
+-  size_t size = (mpz_sizeinbase(n, 2) + 7) / 8;
++  size_t size;
++
++  /* Even moduli are invalid, and not supported by mpz_powm_sec. */
++  if (mpz_even_p (n))
++    return 0;
++
++  size = (mpz_sizeinbase(n, 2) + 7) / 8;
+ 
+   if (size < RSA_MINIMUM_N_OCTETS)
+     return 0;
+diff --git a/testsuite/rsa-test.c b/testsuite/rsa-test.c
+index e9b1c03..a429664 100644
+--- a/testsuite/rsa-test.c
++++ b/testsuite/rsa-test.c
+@@ -57,6 +57,13 @@ test_main(void)
+ 
+   test_rsa_sha512(&pub, &key, expected);
+ 
++  /* Test detection of invalid keys with even modulo */
++  mpz_clrbit (pub.n, 0);
++  ASSERT (!rsa_public_key_prepare (&pub));
++
++  mpz_clrbit (key.p, 0);
++  ASSERT (!rsa_private_key_prepare (&key));
++
+   /* 777-bit key, generated by
+    *
+    *   lsh-keygen -a rsa -l 777 -f advanced-hex
+-- 
+2.7.3
+
diff --git a/package/nettle/nettle.mk b/package/nettle/nettle.mk
index a94a7fc3d..0fbe57b85 100644
--- a/package/nettle/nettle.mk
+++ b/package/nettle/nettle.mk
@@ -13,6 +13,8 @@ NETTLE_LICENSE_FILES = COPYING.LESSERv3 COPYINGv2
 # don't include openssl support for (unused) examples as it has problems
 # with static linking
 NETTLE_CONF_OPTS = --disable-openssl
+# For 0002-fix-CVE-2016-6489.patch
+NETTLE_AUTORECONF = YES
 
 # ARM assembly requires v6+ ISA
 ifeq ($(BR2_ARM_CPU_ARMV4)$(BR2_ARM_CPU_ARMV5)$(BR2_ARM_CPU_ARMV7M),y)