commit e40d1207ebb30dc9549e86c6be9180069a00fefa
author Gilles Peskine <Gilles.Peskine@arm.com> Fri Mar 01 18:08:35 2019 +0100
committer Gilles Peskine <Gilles.Peskine@arm.com> Wed Sep 11 15:46:44 2019 +0200
tree 6707a8354befb972b03da9bb9203139094b734e3
parent f7d6acd4754b732084aea5f0a94ecdc6b4156185

mbedtls_asn1_get_bitstring_null: fix rejection of short inputs

Fix improper rejection of bitstrings with length less than 2.

library/asn1parse.c

diff --git a/library/asn1parse.c b/library/asn1parse.c
index 20e8177..4764ca4 100644
--- a/library/asn1parse.c
+++ b/library/asn1parse.c
@@ -230,8 +230,13 @@
     if( ( ret = mbedtls_asn1_get_tag( p, end, len, MBEDTLS_ASN1_BIT_STRING ) ) != 0 )
         return( ret );
 
-    if( (*len)-- < 2 || *(*p)++ != 0 )
+    if( *len == 0 )
         return( MBEDTLS_ERR_ASN1_INVALID_DATA );
+    --( *len );
+
+    if( **p != 0 )
+        return( MBEDTLS_ERR_ASN1_INVALID_DATA );
+    ++( *p );
 
     return( 0 );
 }