Fix encoding bug in i2c_ASN1_INTEGER

Fix bug where i2c_ASN1_INTEGER mishandles zero if it is marked as
negative.

Thanks to Huzaifa Sidhpurwala <huzaifas@redhat.com> and
Hanno Böck <hanno@hboeck.de> for reporting this issue.

Reviewed-by: Rich Salz <rsalz@openssl.org>

(cherry-picked from a0eed48d37a4b7beea0c966caf09ad46f4a92a44)

Bug: 28175332
Change-Id: I4366a15dee46a02e67746fd1642f2a7bd17f8f84

crypto/asn1/a_int.c

@@ -124,6 +124,8 @@ int i2c_ASN1_INTEGER(ASN1_INTEGER *a, unsigned char **pp)
 		{
 		ret=a->length;
 		i=a->data[0];
+		if (ret == 1 && i == 0)
+			neg = 0;
 		if (!neg && (i > 127)) {
 			pad=1;
 			pb=0;
@@ -157,7 +159,7 @@ int i2c_ASN1_INTEGER(ASN1_INTEGER *a, unsigned char **pp)
 		p += a->length - 1;
 		i = a->length;
 		/* Copy zeros to destination as long as source is zero */
-		while(!*n) {
+		while(!*n && i > 1) {
 			*(p--) = 0;
 			n--;
 			i--;
@@ -415,7 +417,7 @@ ASN1_INTEGER *BN_to_ASN1_INTEGER(const BIGNUM *bn, ASN1_INTEGER *ai)
 		ASN1err(ASN1_F_BN_TO_ASN1_INTEGER,ERR_R_NESTED_ASN1_ERROR);
 		goto err;
 		}
-	if (BN_is_negative(bn))
+	if (BN_is_negative(bn) && !BN_is_zero(bn))
 		ret->type = V_ASN1_NEG_INTEGER;
 	else ret->type=V_ASN1_INTEGER;
 	j=BN_num_bits(bn);

openssl.config

@@ -996,6 +996,7 @@ alpn.patch \
 early_ccs.patch \
 0018-tls_fallback_scsv.patch \
 0019-dsa_double_free.patch \
+0020-encoding_neg_int.patch \
 "
 
 OPENSSL_PATCHES_progs_SOURCES="\

patches/0020-encoding_neg_int.patch

@@ -0,0 +1,50 @@
+From: "Dr. Stephen Henson" <steve@openssl.org>
+Date: Thu, 16 Apr 2015 16:43:09 +0100
+Subject: [PATCH] Fix encoding bug in i2c_ASN1_INTEGER
+
+Fix bug where i2c_ASN1_INTEGER mishandles zero if it is marked as
+negative.
+
+Thanks to Huzaifa Sidhpurwala <huzaifas@redhat.com> and
+Hanno Böck <hanno@hboeck.de> for reporting this issue.
+
+Reviewed-by: Rich Salz <rsalz@openssl.org>
+
+---
+ crypto/asn1/a_int.c | 6 ++++--
+ 1 file changed, 4 insertions(+), 2 deletions(-)
+
+diff --git a/crypto/asn1/a_int.c b/crypto/asn1/a_int.c
+index ad0d250..6574260 100644
+--- a/crypto/asn1/a_int.c
++++ b/crypto/asn1/a_int.c
+@@ -124,6 +124,8 @@ int i2c_ASN1_INTEGER(ASN1_INTEGER *a, unsigned char **pp)
+ 		{
+ 		ret=a->length;
+ 		i=a->data[0];
++		if (ret == 1 && i == 0)
++			neg = 0;
+ 		if (!neg && (i > 127)) {
+ 			pad=1;
+ 			pb=0;
+@@ -157,7 +159,7 @@ int i2c_ASN1_INTEGER(ASN1_INTEGER *a, unsigned char **pp)
+ 		p += a->length - 1;
+ 		i = a->length;
+ 		/* Copy zeros to destination as long as source is zero */
+-		while(!*n) {
++		while(!*n && i > 1) {
+ 			*(p--) = 0;
+ 			n--;
+ 			i--;
+@@ -415,7 +417,7 @@ ASN1_INTEGER *BN_to_ASN1_INTEGER(const BIGNUM *bn, ASN1_INTEGER *ai)
+ 		ASN1err(ASN1_F_BN_TO_ASN1_INTEGER,ERR_R_NESTED_ASN1_ERROR);
+ 		goto err;
+ 		}
+-	if (BN_is_negative(bn))
++	if (BN_is_negative(bn) && !BN_is_zero(bn))
+ 		ret->type = V_ASN1_NEG_INTEGER;
+ 	else ret->type=V_ASN1_INTEGER;
+ 	j=BN_num_bits(bn);
+-- 
+2.8.0.rc3.226.g39d4020
+