commit f4b3429782c66d439d20616229bffe3d226a73f4
author Gilles Peskine <Gilles.Peskine@arm.com> Sat Jan 30 13:05:32 2021 +0100
committer Gilles Peskine <Gilles.Peskine@arm.com> Mon Feb 22 19:24:03 2021 +0100
tree 9ed0994497196ed8c3ee9ff285f5b61039c0ac9d
parent 39a1a26d0b6036832632baf99a240f35bef0b105

Fix mutex leak in CTR_DRBG

mbedtls_ctr_drbg_free() left a mutex in the initialized state. This
caused a resource leak on platforms where mbedtls_mutex_init()
allocates resources.

To fix this, mbedtls_ctr_drbg_free() no longer reinitializes the
mutex. To preserve the property that mbedtls_ctr_drbg_free() leaves
the object in an initialized state, which is generally true throughout
the library except regarding mutex objects on some platforms, no
longer initialize the mutex in mbedtls_ctr_drbg_init(). Since the
mutex is only used after seeding, and seeding is only permitted once,
call mbedtls_mutex_init() as part of the seeding process.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

library/ctr_drbg.c

diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 3815dc7..48efada 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -56,10 +56,6 @@
     ctx->reseed_counter = -1;
 
     ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
-
-#if defined(MBEDTLS_THREADING_C)
-    mbedtls_mutex_init( &ctx->mutex );
-#endif
 }
 
 /*
@@ -72,15 +68,13 @@
         return;
 
 #if defined(MBEDTLS_THREADING_C)
-    mbedtls_mutex_free( &ctx->mutex );
+    if( ctx->f_entropy != NULL )
+        mbedtls_mutex_free( &ctx->mutex );
 #endif
     mbedtls_aes_free( &ctx->aes_ctx );
     mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ctr_drbg_context ) );
     ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
     ctx->reseed_counter = -1;
-#if defined(MBEDTLS_THREADING_C)
-    mbedtls_mutex_init( &ctx->mutex );
-#endif
 }
 
 void mbedtls_ctr_drbg_set_prediction_resistance( mbedtls_ctr_drbg_context *ctx,
@@ -464,6 +458,10 @@
 
     memset( key, 0, MBEDTLS_CTR_DRBG_KEYSIZE );
 
+#if defined(MBEDTLS_THREADING_C)
+    mbedtls_mutex_init( &ctx->mutex );
+#endif
+
     mbedtls_aes_init( &ctx->aes_ctx );
 
     ctx->f_entropy = f_entropy;