From bffefae305adfe899984c558111cd02b8cfdb31d Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Mon, 5 Nov 2018 12:47:16 +0000
Subject: [PATCH] Safe-guard `ssl_conf_remove_psk()` for simultaneous
 raw-opaque PSKs

The code maintains the invariant that raw and opaque PSKs are never
configured simultaneously, so strictly speaking `ssl_conf_remove_psk()`
need not consider clearing the raw PSK if it has already cleared an
opaque one - and previously, it didn't. However, it doesn't come at
any cost to keep this check as a safe-guard to future unforeseen
situations where opaque and raw PSKs _are_ both present.
---
 library/ssl_tls.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 8f3d203de..6fa2e3a76 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -7426,7 +7426,11 @@ static void ssl_conf_remove_psk( mbedtls_ssl_config *conf )
          * user's responsibility. */
         conf->psk_opaque = 0;
     }
-    else
+    /* This and the following branch should never
+     * be taken simultaenously as we maintain the
+     * invariant that raw and opaque PSKs are never
+     * configured simultaneously. As a safeguard,
+     * though, `else` is omitted here. */
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
     if( conf->psk != NULL )
     {