Fix a NULL dereference in GENERAL_NAME_cmp()

Comparing two GENERAL_NAME structures containing an EDIPARTYNAME can lead
to a crash. This enables a denial of service attack for an attacker who can
control both sides of the comparison.

Issue reported to OpenSSL on Nov 9 by David Benjamin.
OpenSSL shared the information with us on Dec 1st.
Fix from Matt Caswell (OpenSSL) with a few small tweaks.

ok jsing

1 files changed, 21 insertions, 1 deletions

diff --git a/lib/libcrypto/asn1/tasn_dec.c b/lib/libcrypto/asn1/tasn_dec.c
index 70dc355ca1f..4b08e90404a 100644
--- a/lib/libcrypto/asn1/tasn_dec.c
+++ b/lib/libcrypto/asn1/tasn_dec.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tasn_dec.c,v 1.37 2019/04/01 15:48:04 jsing Exp $ */
+/* $OpenBSD: tasn_dec.c,v 1.38 2020/12/08 15:06:42 tb Exp $ */
 /* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
  * project 2000.
  */
@@ -210,6 +210,16 @@ asn1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
 		break;
 
 	case ASN1_ITYPE_MSTRING:
+		/*
+		 * It never makes sense for multi-strings to have implicit
+		 * tagging, so if tag != -1, then this looks like an error in
+		 * the template.
+		 */
+		if (tag != -1) {
+			ASN1error(ASN1_R_BAD_TEMPLATE);
+			goto err;
+		}
+
 		p = *in;
 		/* Just read in tag and class */
 		ret = asn1_check_tlen(NULL, &otag, &oclass, NULL, NULL,
@@ -245,6 +255,16 @@ asn1_item_ex_d2i(ASN1_VALUE **pval, const unsigned char **in, long len,
 		    it, tag, aclass, opt, ctx);
 
 	case ASN1_ITYPE_CHOICE:
+		/*
+		 * It never makes sense for CHOICE types to have implicit
+		 * tagging, so if tag != -1, then this looks like an error in
+		 * the template.
+		 */
+		if (tag != -1) {
+			ASN1error(ASN1_R_BAD_TEMPLATE);
+			goto err;
+		}
+
 		if (asn1_cb && !asn1_cb(ASN1_OP_D2I_PRE, pval, it, NULL))
 			goto auxerr;