commit d81b5ae238bbde7df98d9e91d4b36521f32c38f7
author Gilles Peskine <gilles.peskine@arm.com> Tue Apr 12 11:05:26 2022 +0200
committer GitHub <noreply@github.com> Tue Apr 12 11:05:26 2022 +0200
tree 663d51d62cc3571a65e44c47f5fc8a562aa5d2bf
parent 50b677d9e5b4583785b4106db488eb2ae6eff15c
parent 28fd4cd8e91897c18346a41a5f07019fb0902fbe

Merge pull request #5717 from daverodgman/backport_2.28-alert_reentrant

Backport 2.28 - 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 0b696dd..0b1322d 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -4918,6 +4918,9 @@
     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 ));
 
@@ -5790,9 +5793,6 @@
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write close notify" ) );
 
-    if( ssl->out_left != 0 )
-        return( mbedtls_ssl_flush_output( ssl ) );
-
     if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER )
     {
         if( ( ret = mbedtls_ssl_send_alert_message( ssl,