Fix x509_get_subject_alt_name to drop invalid tag
Fix the x509_get_subject_alt_name() function to not accept invalid
tags. The problem was that the ASN.1 class for tags consists of two
bits. Simply doing bit-wise and of the CONTEXT_SPECIFIC macro with the
input tag has the potential of accepting tag values 0x10 (private)
which would indicate that the certificate has an incorrect format.
diff --git a/library/x509_crt.c b/library/x509_crt.c
index 8cb1923..5529366 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -472,9 +472,12 @@
if( ( ret = mbedtls_asn1_get_len( p, end, &tag_len ) ) != 0 )
return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
- if( ( tag & MBEDTLS_ASN1_CONTEXT_SPECIFIC ) != MBEDTLS_ASN1_CONTEXT_SPECIFIC )
+ if( ( tag & MBEDTLS_ASN1_TAG_CLASS_MASK ) !=
+ MBEDTLS_ASN1_CONTEXT_SPECIFIC )
+ {
return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
+ }
/* Skip everything but DNS name */
if( tag != ( MBEDTLS_ASN1_CONTEXT_SPECIFIC | 2 ) )