commit 43b09437366e0fc341044308bf8e3afd2509bed3
author Gilles Peskine <gilles.peskine@arm.com> Tue Apr 12 11:05:20 2022 +0200
committer GitHub <noreply@github.com> Tue Apr 12 11:05:20 2022 +0200
tree 9299bf6755a91c3672bd53af5176a5ce282e4a28
parent ed35887fc8591ce3bc389194b4f53ad80c817a84
parent f945e0a475b018fb6cab14201d8da0bd55343cb7

Merge pull request #1946 from hanno-arm/alert_reentrant

Make mbedtls_ssl_send_alert_message() reentrant

ChangeLog.d/alert_reentrant.txt

diff --git a/ChangeLog.d/alert_reentrant.txt b/ChangeLog.d/alert_reentrant.txt
new file mode 100644
index 0000000..691d64c
--- /dev/null
+++ b/ChangeLog.d/alert_reentrant.txt
@@ -0,0 +1,5 @@
+Bugfix
+   * Fix bug in the alert sending function mbedtls_ssl_send_alert_message()
+     potentially leading to corrupted alert messages being sent in case
+     the function needs to be re-called after initially returning
+     MBEDTLS_SSL_WANT_WRITE. Fixes #1916.

library/ssl_msg.c

diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 4eac24b..051e4b0 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -4855,6 +4855,9 @@
     if( ssl == NULL || ssl->conf == NULL )
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
 
+    if( ssl->out_left != 0 )
+        return( mbedtls_ssl_flush_output( ssl ) );
+
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> send alert message" ) );
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "send alert level=%u message=%u", level, message ));
 
@@ -5714,9 +5717,6 @@
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write close notify" ) );
 
-    if( ssl->out_left != 0 )
-        return( mbedtls_ssl_flush_output( ssl ) );
-
     if( mbedtls_ssl_is_handshake_over( ssl ) == 1 )
     {
         if( ( ret = mbedtls_ssl_send_alert_message( ssl,