Add a semantic patch to prevent use after free.

scripts/cocci/null-after-free.cocci

@@ -0,0 +1,84 @@
+// Read a list of 'free' type function names from stdin, if stdin is a pipe.
+@initialize:python@
+@@
+import sys
+functions = set(['free'])
+if not sys.stdin.isatty():
+    for line in sys.stdin:
+        f = line.rstrip('\n')
+        functions.add(f)
+
+// Match all function names.
+@a@
+identifier F;
+@@
+    F(...)
+
+// Match all function names in the set.
+@script:python b depends on a@
+F << a.F;
+f;
+@@
+if F in functions:
+    coccinelle.f = F
+    cocci.include_match(True)
+
+// Remove casts.
+@@
+identifier b.f;
+type t;
+expression x;
+@@
+-   f((t *)(x))
++   f(x)
+
+// Add NULL assignment after free, if absent.
+@@
+identifier b.f;
+expression x;
+@@
+(
+    f(x);
+    x = NULL;
+|
+    f(x);
++   x = NULL;
+)
+
+// Remove NULL assignments to local variables.
+@@
+local idexpression x;
+@@
+-   x = NULL;
+    ... when != x
+
+// Remove NULL assignments followed later by another assignment.
+@@
+idexpression x;
+identifier y;
+@@
+(
+-   x = NULL;
+    ... when != x
+    x = ...;
+|
+-   x->y = NULL;
+    ... when != x->y
+    x->y = ...;
+)
+
+// Remove NULL assignments followed immediately by another assignment.
+@@
+expression z;
+@@
+-   z = NULL;
+    z = ...;
+
+// Remove NULL assignments to structure members before the structure is freed.
+@@
+identifier b.f;
+identifier x, y;
+@@
+-   x->y = NULL;
+    ... when != x
+    f(x);

scripts/cocci/themis-free-functions.txt

@@ -0,0 +1,12 @@
+soter_hash_destroy
+soter_rsa_key_pair_gen_destroy
+soter_sym_ctx_destroy
+soter_asym_cipher_destroy
+soter_hmac_destroy
+soter_sign_destroy
+soter_verify_destroy
+themis_message_destroy
+themis_secure_message_ec_encrypter_destroy
+themis_secure_message_rsa_encrypter_destroy
+themis_secure_message_signer_destroy
+themis_secure_message_verifier_destroy

src/soter/soter_hmac.c

@@ -59,12 +59,14 @@ soter_status_t soter_hmac_init(soter_hmac_ctx_t* hmac_ctx,
         res = soter_hash_update(hmac_ctx->hash_ctx, key, key_length);
         if (SOTER_SUCCESS != res) {
             soter_hash_destroy(hmac_ctx->hash_ctx);
+            hmac_ctx->hash_ctx = NULL;
             return res;
         }
 
         res = soter_hash_final(hmac_ctx->hash_ctx, hmac_ctx->o_key_pad, &o_key_pad_length);
         if (SOTER_SUCCESS != res) {
             soter_hash_destroy(hmac_ctx->hash_ctx);
+            hmac_ctx->hash_ctx = NULL;
             return res;
         }
     } else {
@@ -88,12 +90,14 @@ soter_status_t soter_hmac_init(soter_hmac_ctx_t* hmac_ctx,
     res = soter_hash_init(hmac_ctx->hash_ctx, algo);
     if (res != SOTER_SUCCESS) {
         soter_hash_destroy(hmac_ctx->hash_ctx);
+        hmac_ctx->hash_ctx = NULL;
         return SOTER_FAIL;
     }
 
     res = soter_hash_update(hmac_ctx->hash_ctx, i_key_pad, block_size);
     if (SOTER_SUCCESS != res) {
         soter_hash_destroy(hmac_ctx->hash_ctx);
+        hmac_ctx->hash_ctx = NULL;
         soter_hmac_cleanup(hmac_ctx);
         return res;
     }

src/themis/message.c

@@ -79,6 +79,5 @@ themis_status_t themis_message_destroy(themis_message_t* ctx)
         free(ctx->data);
     }
     free(ctx);
-    ctx = NULL;
     return THEMIS_SUCCESS;
 }

src/themis/secure_message_wrapper.c

@@ -55,7 +55,6 @@ themis_secure_message_signer_t* themis_secure_message_signer_init(const uint8_t*
     if (!ctx) {
         return NULL;
     }
-    ctx->sign_ctx = NULL;
     ctx->sign_ctx = soter_sign_create(get_alg_id(key, key_length), NULL, 0, key, key_length);
     if (!(ctx->sign_ctx)) {
         free(ctx);
@@ -117,7 +116,6 @@ themis_status_t themis_secure_message_signer_proceed(themis_secure_message_signe
 themis_status_t themis_secure_message_signer_destroy(themis_secure_message_signer_t* ctx)
 {
     soter_sign_destroy(ctx->sign_ctx);
-    ctx->sign_ctx = NULL;
     free(ctx);
     return THEMIS_SUCCESS;
 }