From c6b5d833ec650dea86e471df2c470829c71c8b5f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?= <mpg2@elzevir.fr>
Date: Thu, 27 Aug 2015 16:37:35 +0200
Subject: [PATCH] Fix handling of long PSK identities

fixes #238
---
 ChangeLog         |  3 +++
 library/ssl_cli.c | 22 ++++++++++++++++++++++
 library/ssl_tls.c |  7 +++++++
 3 files changed, 32 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 8677ad9d5..a4772e011 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -30,6 +30,9 @@ Bugfix
      result trying to unlock an unlocked mutex on invalid input (found by
      Fredrik Axelsson) (#257)
    * Fix -Wshadow warnings (found by hnrkp) (#240)
+   * Fix memory corruption on client with overlong PSK identity, around
+     SSL_MAX_CONTENT_LEN or higher - not triggerrable remotely (found by
+     Aleksandrs Saveljevs) (#238)
 
 Changes
    * The PEM parser now accepts a trailing space at end of lines (#226).
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index c6f810cd7..75983d19e 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1748,6 +1748,12 @@ static int ssl_write_encrypted_pms( mbedtls_ssl_context *ssl,
     size_t len_bytes = ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 ? 0 : 2;
     unsigned char *p = ssl->handshake->premaster + pms_offset;
 
+    if( offset + len_bytes > MBEDTLS_SSL_MAX_CONTENT_LEN )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small for encrypted pms" ) );
+        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+    }
+
     /*
      * Generate (part of) the pre-master as
      *  struct {
@@ -2522,6 +2528,14 @@ static int ssl_write_client_key_exchange( mbedtls_ssl_context *ssl )
 
         i = 4;
         n = ssl->conf->psk_identity_len;
+
+        if( i + 2 + n > MBEDTLS_SSL_MAX_CONTENT_LEN )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "psk identity too long or "
+                                        "SSL buffer too short" ) );
+            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+        }
+
         ssl->out_msg[i++] = (unsigned char)( n >> 8 );
         ssl->out_msg[i++] = (unsigned char)( n      );
 
@@ -2550,6 +2564,14 @@ static int ssl_write_client_key_exchange( mbedtls_ssl_context *ssl )
              * ClientDiffieHellmanPublic public (DHM send G^X mod P)
              */
             n = ssl->handshake->dhm_ctx.len;
+
+            if( i + 2 + n > MBEDTLS_SSL_MAX_CONTENT_LEN )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "psk identity or DHM size too long"
+                                            " or SSL buffer too short" ) );
+                return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+            }
+
             ssl->out_msg[i++] = (unsigned char)( n >> 8 );
             ssl->out_msg[i++] = (unsigned char)( n      );
 
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 80dbe8a7d..793d2415e 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5457,6 +5457,13 @@ int mbedtls_ssl_conf_psk( mbedtls_ssl_config *conf,
     if( psk_len > MBEDTLS_PSK_MAX_LEN )
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
 
+    /* Identity len will be encoded on two bytes */
+    if( ( psk_identity_len >> 16 ) != 0 ||
+        psk_identity_len > MBEDTLS_SSL_MAX_CONTENT_LEN )
+    {
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    }
+
     if( conf->psk != NULL || conf->psk_identity != NULL )
     {
         mbedtls_free( conf->psk );