Make X.509 CRT cache reference counting unconditional
Previously, reference counting for the CRT frames and PK contexts
handed out by mbedtls_x509_crt_{frame|pk}_acquire() was implemented
only in case threading support was enabled, which leaves the door
open for a potential use-after-free should a single-threaded application
use nested calls to mbedtls_x509_crt_acquire().
Since Mbed TLS itself does not use such nested calls, it might be
preferred long-term to forbid nesting of acquire calls on the API
level, and hence get rid of reference counting in the interest of
code-size benefits. However, this can be considered as an optimization
of X.509 on demand parsing, and for now this commit introduces
reference counting unconditionally to have a safe version of
on demand parsing to build further optimizations upon.
diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index 6db9bc9..85943c7 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -831,19 +831,17 @@
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_lock( &crt->cache->frame_mutex ) != 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif /* MBEDTLS_THREADING_C */
if( crt->cache->frame_readers == 0 )
-#endif /* MBEDTLS_THREADING_C */
- {
ret = mbedtls_x509_crt_cache_provide_frame( crt );
- }
-#if defined(MBEDTLS_THREADING_C)
if( crt->cache->frame_readers == MBEDTLS_X509_CACHE_FRAME_READERS_MAX )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
crt->cache->frame_readers++;
+#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_unlock( &crt->cache->frame_mutex ) != 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
#endif /* MBEDTLS_THREADING_C */
@@ -864,12 +862,14 @@
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_lock( &crt->cache->frame_mutex ) != 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif /* MBEDTLS_THREADING_C */
if( crt->cache->frame_readers == 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
crt->cache->frame_readers--;
+#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_unlock( &crt->cache->frame_mutex );
#endif /* MBEDTLS_THREADING_C */
@@ -919,19 +919,17 @@
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_lock( &crt->cache->pk_mutex ) != 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif /* MBEDTLS_THREADING_C */
if( crt->cache->pk_readers == 0 )
-#endif /* MBEDTLS_THREADING_C */
- {
ret = mbedtls_x509_crt_cache_provide_pk( crt );
- }
-#if defined(MBEDTLS_THREADING_C)
if( crt->cache->pk_readers == MBEDTLS_X509_CACHE_PK_READERS_MAX )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
crt->cache->pk_readers++;
+#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_unlock( &crt->cache->pk_mutex ) != 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
#endif /* MBEDTLS_THREADING_C */
@@ -952,12 +950,14 @@
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_lock( &crt->cache->pk_mutex ) != 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif /* MBEDTLS_THREADING_C */
if( crt->cache->pk_readers == 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
crt->cache->pk_readers--;
+#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_unlock( &crt->cache->pk_mutex );
#endif /* MBEDTLS_THREADING_C */
diff --git a/include/mbedtls/x509_internal.h b/include/mbedtls/x509_internal.h
index bed9772..7729108 100644
--- a/include/mbedtls/x509_internal.h
+++ b/include/mbedtls/x509_internal.h
@@ -37,9 +37,9 @@
#define MBEDTLS_X509_CACHE_FRAME_READERS_MAX ((uint32_t) -1)
typedef struct mbedtls_x509_crt_cache
{
-#if defined(MBEDTLS_THREADING_C)
uint32_t frame_readers;
uint32_t pk_readers;
+#if defined(MBEDTLS_THREADING_C)
mbedtls_threading_mutex_t frame_mutex;
mbedtls_threading_mutex_t pk_mutex;
#endif