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From ed282e9a463c068146c945984fdea7828e663861 Mon Sep 17 00:00:00 2001
From: Tobias Brunner <tobias@strongswan.org>
Date: Mon, 29 May 2017 11:59:34 +0200
Subject: [PATCH] gmp: Fix RSA signature verification for m >= n

By definition, m must be <= n-1, we didn't enforce that and because
mpz_export() returns NULL if the passed value is zero a crash could have
been triggered with m == n.

Fixes CVE-2017-11185.
---
 src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c b/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
index 32a72ac9600b..a741f85d4f62 100644
--- a/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
+++ b/src/libstrongswan/plugins/gmp/gmp_rsa_public_key.c
@@ -78,11 +78,17 @@ static chunk_t rsaep(private_gmp_rsa_public_key_t *this, chunk_t data)
 	mpz_t m, c;
 	chunk_t encrypted;
 
-	mpz_init(c);
 	mpz_init(m);
-
 	mpz_import(m, data.len, 1, 1, 1, 0, data.ptr);
 
+	if (mpz_cmp_ui(m, 0) <= 0 || mpz_cmp(m, this->n) >= 0)
+	{	/* m must be <= n-1, but 0 is a valid value, doesn't really make sense
+		 * here, though */
+		mpz_clear(m);
+		return chunk_empty;
+	}
+
+	mpz_init(c);
 	mpz_powm(c, m, this->e, this->n);
 
 	encrypted.len = this->k;
@@ -150,7 +156,7 @@ static bool verify_emsa_pkcs1_signature(private_gmp_rsa_public_key_t *this,
 	 */
 
 	/* check magic bytes */
-	if (*(em.ptr) != 0x00 || *(em.ptr+1) != 0x01)
+	if (em.len < 2 || *(em.ptr) != 0x00 || *(em.ptr+1) != 0x01)
 	{
 		goto end;
 	}
-- 
2.7.4