Add check for lengths over 65535 in mbedtls_asn1_write_len()
diff --git a/include/mbedtls/asn1write.h b/include/mbedtls/asn1write.h
index 73ff32b..4d2917e 100644
--- a/include/mbedtls/asn1write.h
+++ b/include/mbedtls/asn1write.h
@@ -40,6 +40,8 @@
* \param start start of the buffer (for bounds-checking)
* \param len the length to write
*
+ * \note lengths over 65535 are not supported at the moment
+ *
* \return the length written or a negative error code
*/
int mbedtls_asn1_write_len( unsigned char **p, unsigned char *start, size_t len );
diff --git a/library/asn1write.c b/library/asn1write.c
index 027c858..ef35ee4 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -41,6 +41,11 @@
int mbedtls_asn1_write_len( unsigned char **p, unsigned char *start, size_t len )
{
+ // We don't support lengths over 65535 for now
+ //
+ if( len > 0xFFFF )
+ return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
+
if( len < 0x80 )
{
if( *p - start < 1 )
@@ -63,8 +68,6 @@
if( *p - start < 3 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
- // We assume we never have lengths larger than 65535 bytes
- //
*--(*p) = len % 256;
*--(*p) = ( len / 256 ) % 256;
*--(*p) = 0x82;