From 0af25e71ab0a3c24ca57feeb5af42b092c269a64 Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Mon, 15 Oct 2018 12:13:38 +0100
Subject: [PATCH 1/2] Add parentheses about parameter of MBEDTLS_X509_ID_FLAG

The `id` parameter of the public `MBEDTLS_X509_ID_FLAG` macro was
used in a subtraction without being surrounded by parentheses.
Since some operators bind less strongly than subtraction, this
could lead to erroneous evaluation of `MBEDTLS_X509_ID_FLAG`.
For example, `MBEDTLS_X509_ID_FLAG( 1 << 2 )` would evaluate
evaluate to

  `1 << ( 1 << 2 - 1 ) == 1 << ( 1 << 1 ) == 4`

instead of the intended

  `1 << ( ( 1 << 2 ) - 1 ) == 1 << ( 4 - 1 ) == 8`.

This commit fixes this by adding parentheses about the `id`
parameter in the definition of `MBEDTLS_X509_ID_FLAG`.
---
 include/mbedtls/x509_crt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index ac23cffe84..d725e29ea6 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -98,7 +98,7 @@ mbedtls_x509_crt;
  * Build flag from an algorithm/curve identifier (pk, md, ecp)
  * Since 0 is always XXX_NONE, ignore it.
  */
-#define MBEDTLS_X509_ID_FLAG( id )   ( 1 << ( id - 1 ) )
+#define MBEDTLS_X509_ID_FLAG( id )   ( 1 << ( ( id ) - 1 ) )
 
 /**
  * Security profile for certificate verification.

From b2ba79abec90aa64cfc48b8dcdacbf5751d77a7f Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Mon, 15 Oct 2018 12:23:02 +0100
Subject: [PATCH 2/2] Adapt ChangeLog

---
 ChangeLog | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 0a9dc4f8d0..b8f42e84b5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,10 @@ Bugfix
      MBEDTLS_THREADING_C is defined. Found by TrinityTonic, #1095
    * Fix a bug in the update function for SSL ticket keys which previously
      invalidated keys of a lifetime of less than a 1s. Fixes #1968.
+   * Add missing parentheses around parameters in the definition of the
+     public macro MBEDTLS_X509_ID_FLAG. This could lead to invalid evaluation
+     in case operators binding less strongly than subtraction were used
+     for the parameter.
 
 Changes
    * Add tests for session resumption in DTLS.