commit fbe6f498cdb6c01331afb9bc11c05cb95a3548e5
author David Benjamin <davidben@chromium.org> Tue Oct 21 00:45:25 2014 -0400
committer Adam Langley <agl@google.com> Fri Oct 24 18:26:11 2014 +0000
tree e2d72c48d0a4e685414fb7fd843882def34037ea
parent b5b685496891feb1ea0fe2e7d9a7cfcffd7f1f4f

The empty contents are not a valid ASN.1 INTEGER.

Zero is encoded as a single zero octet. Per X.690, 8.3.1:

  The encoding of an integer value shall be primitive. The contents octets
  shall consist of one or more octets.

Change-Id: If4304a2be5117b71446a3a62a2b8a6124f85a202
Reviewed-on: https://boringssl-review.googlesource.com/2010
Reviewed-by: Adam Langley <agl@google.com>

crypto/bytestring/bytestring_test.c

diff --git a/crypto/bytestring/bytestring_test.c b/crypto/bytestring/bytestring_test.c
index da30dbb..43c99dc 100644
--- a/crypto/bytestring/bytestring_test.c
+++ b/crypto/bytestring/bytestring_test.c
@@ -467,6 +467,8 @@
 static const ASN1_INVALID_UINT64_TEST kAsn1InvalidUint64Tests[] = {
   /* Bad tag. */
   {"\x03\x01\x00", 3},
+  /* Empty contents. */
+  {"\x02\x00", 2},
   /* Negative number. */
   {"\x02\x01\x80", 3},
   /* Overflow */

crypto/bytestring/cbs.c

diff --git a/crypto/bytestring/cbs.c b/crypto/bytestring/cbs.c
index 07cc126..1d1da88 100644
--- a/crypto/bytestring/cbs.c
+++ b/crypto/bytestring/cbs.c
@@ -284,7 +284,12 @@
   data = CBS_data(&bytes);
   len = CBS_len(&bytes);
 
-  if (len > 0 && (data[0] & 0x80) != 0) {
+  if (len == 0) {
+    /* An INTEGER is encoded with at least one octet. */
+    return 0;
+  }
+
+  if ((data[0] & 0x80) != 0) {
     /* negative number */
     return 0;
   }