From 740b218386083dc708ce98ccc94a63a95cd5629e Mon Sep 17 00:00:00 2001
From: Krzysztof Stachowiak <krzysiek.stachowiak@gmail.com>
Date: Tue, 13 Mar 2018 11:31:14 +0100
Subject: [PATCH 1/3] Add bounds check before length read

---
 library/ssl_cli.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 2534346a49..585750ef2e 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -2057,6 +2057,12 @@ static int ssl_parse_server_psk_hint( mbedtls_ssl_context *ssl,
      *
      * opaque psk_identity_hint<0..2^16-1>;
      */
+    if( (*p) > end - 2 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message "
+                                    "(psk_identity_hint length)" ) );
+        return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
+    }
     len = (*p)[0] << 8 | (*p)[1];
     *p += 2;
 

From 5224a7544c95552553e2e6be0b4a789956a6464e Mon Sep 17 00:00:00 2001
From: Krzysztof Stachowiak <krzysiek.stachowiak@gmail.com>
Date: Tue, 13 Mar 2018 11:31:38 +0100
Subject: [PATCH 2/3] Prevent arithmetic overflow on bounds check

---
 library/ssl_cli.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 585750ef2e..759a4562a1 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -2066,7 +2066,7 @@ static int ssl_parse_server_psk_hint( mbedtls_ssl_context *ssl,
     len = (*p)[0] << 8 | (*p)[1];
     *p += 2;
 
-    if( (*p) + len > end )
+    if( (*p) > end - len )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message "
                                     "(psk_identity_hint length)" ) );

From 7fa1ae70c85e847fcd5e434b1417c8dc4cc62c72 Mon Sep 17 00:00:00 2001
From: Krzysztof Stachowiak <krzysiek.stachowiak@gmail.com>
Date: Tue, 13 Mar 2018 17:17:38 +0100
Subject: [PATCH 3/3] Add Changelog entry

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

diff --git a/ChangeLog b/ChangeLog
index dfd34bf69a..585c81a1e6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -17,6 +17,8 @@ Security
      implementation allowed an offline 2^80 brute force attack on the
      HMAC key of a single, uninterrupted connection (with no
      resumption of the session).
+   * Fix a buffer overread in ssl_parse_server_psk_hint() that could cause a
+     crash on invalid input.
 
 Features
    * Extend PKCS#8 interface by introducing support for the entire SHA
@@ -44,6 +46,8 @@ Bugfix
      Nick Wilson on issue #355
    * In test_suite_pk, pass valid parameters when testing for hash length
      overflow. #1179
+   * Fix a possible arithmetic overflow in ssl_parse_server_psk_hint() that
+     could cause a key exchange to fail on valid data.
 
 Changes
    * Fix tag lengths and value ranges in the documentation of CCM encryption.