From ba2fda645affceb7fafde8aa0624ccf12a5e59e7 Mon Sep 17 00:00:00 2001
From: Andres Amaya Garcia <Andres.AmayaGarcia@arm.com>
Date: Tue, 17 Jan 2017 23:24:02 +0000
Subject: [PATCH] Fix integer overflows in buffer bound checks

Fix potential integer overflows in the following functions:
  * mbedtls_md2_update() to be bypassed and cause
  * mbedtls_cipher_update()
  * mbedtls_ctr_drbg_reseed()
This overflows would mainly be exploitable in 32-bit systems and could
cause buffer bound checks to be bypassed.
---
 ChangeLog          | 10 ++++++++++
 library/cipher.c   |  4 ++--
 library/ctr_drbg.c |  3 ++-
 library/md2.c      |  2 +-
 4 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 92d7977e0..0776a56d8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS 2.x.x branch released xxxx-xx-xx
+
+Bugfix
+   * Fixed potential arithmetic overflow in mbedtls_ctr_drbg_reseed() that could
+     cause buffer bound checks to be bypassed. Found by Eyal Itkin.
+   * Fixed potential arithmetic overflows in mbedtls_cipher_update() that could
+     cause buffer bound checks to be bypassed. Found by Eyal Itkin.
+   * Fixed potential arithmetic overflow in mbedtls_md2_update() that could
+     cause buffer bound checks to be bypassed. Found by Eyal Itkin.
+
 = mbed TLS 2.1.6 branch released 2016-10-17
 
 Security
diff --git a/library/cipher.c b/library/cipher.c
index ccc068503..1523b07da 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -300,9 +300,9 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
          * If there is not enough data for a full block, cache it.
          */
         if( ( ctx->operation == MBEDTLS_DECRYPT &&
-                ilen + ctx->unprocessed_len <= mbedtls_cipher_get_block_size( ctx ) ) ||
+                ilen <= mbedtls_cipher_get_block_size( ctx ) - ctx->unprocessed_len ) ||
              ( ctx->operation == MBEDTLS_ENCRYPT &&
-                ilen + ctx->unprocessed_len < mbedtls_cipher_get_block_size( ctx ) ) )
+                ilen < mbedtls_cipher_get_block_size( ctx ) - ctx->unprocessed_len ) )
         {
             memcpy( &( ctx->unprocessed_data[ctx->unprocessed_len] ), input,
                     ilen );
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index aefddfa1d..646196eb1 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -290,7 +290,8 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
     unsigned char seed[MBEDTLS_CTR_DRBG_MAX_SEED_INPUT];
     size_t seedlen = 0;
 
-    if( ctx->entropy_len + len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT )
+    if( ctx->entropy_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT ||
+        len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - ctx->entropy_len )
         return( MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG );
 
     memset( seed, 0, MBEDTLS_CTR_DRBG_MAX_SEED_INPUT );
diff --git a/library/md2.c b/library/md2.c
index 897670131..95cbcce65 100644
--- a/library/md2.c
+++ b/library/md2.c
@@ -158,7 +158,7 @@ void mbedtls_md2_update( mbedtls_md2_context *ctx, const unsigned char *input, s
 
     while( ilen > 0 )
     {
-        if( ctx->left + ilen > 16 )
+        if( ilen > 16 - ctx->left )
             fill = 16 - ctx->left;
         else
             fill = ilen;