From 67ae0b983992c8d3e6f348670736e3a292984257 Mon Sep 17 00:00:00 2001
From: Andres AG <andres.amayagarcia@arm.com>
Date: Mon, 19 Sep 2016 16:58:45 +0100
Subject: [PATCH] Fix sig->tag update in mbedtls_x509_get_sig()

---
 ChangeLog      | 3 +++
 library/x509.c | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index f53530d37..05e3f9dde 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -20,6 +20,9 @@ Bugfix
    * Fix documentation and implementation missmatch for function arguments of
      mbedtls_gcm_finish(). Found by cmiatpaar. #602
    * Guarantee that P>Q at RSA key generation. Found by inestlerode. #558
+   * Fix mbedtls_x509_get_sig() to update the ASN1 type in the mbedtls_x509_buf
+     data structure until after error checks are successful. Found by
+     subramanyam-c.
 
 = mbed TLS 1.3.17 branch 2016-06-28
 
diff --git a/library/x509.c b/library/x509.c
index ab105d8fa..282a95190 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -559,16 +559,18 @@ int x509_get_sig( unsigned char **p, const unsigned char *end, x509_buf *sig )
 {
     int ret;
     size_t len;
+    int tag_type;
 
     if( ( end - *p ) < 1 )
         return( POLARSSL_ERR_X509_INVALID_SIGNATURE +
                 POLARSSL_ERR_ASN1_OUT_OF_DATA );
 
-    sig->tag = **p;
+    tag_type = **p;
 
     if( ( ret = asn1_get_bitstring_null( p, end, &len ) ) != 0 )
         return( POLARSSL_ERR_X509_INVALID_SIGNATURE + ret );
 
+    sig->tag = tag_type;
     sig->len = len;
     sig->p = *p;