commit 6a54336897e5150b95c64bf1eea122cdd9556a9c
author Andres Amaya Garcia <Andres.AmayaGarcia@arm.com> Tue Jan 17 23:04:22 2017 +0000
committer Simon Butcher <simon.butcher@arm.com> Wed Feb 15 23:31:07 2017 +0200
tree 09756beb852437c77e72cc74c3314c9fb0428668
parent 49d29337facd93e5d1039b7073ded21ec6dde54d

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.

library/ctr_drbg.c

diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 386f8ad..55612c7 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -290,7 +290,8 @@
     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 );