Fix double free in DSA private key parsing.

Fix double free bug when parsing malformed DSA private keys.

Thanks to Adam Langley (Google/BoringSSL) for discovering this bug using
libFuzzer.

CVE-2016-0705

Reviewed-by: Emilia Käsper <emilia@openssl.org>

diff --git a/crypto/dsa/dsa_ameth.c b/crypto/dsa/dsa_ameth.c
index e385dd3a6ffae4dbe1fd1f77ceb2e406247676fd..cc83d6e6ad3b6f7acc4f640b43760fdf7eee4236 100644 (file)
--- a/crypto/dsa/dsa_ameth.c
+++ b/crypto/dsa/dsa_ameth.c
@@ -191,6 +191,8 @@ static int dsa_priv_decode(EVP_PKEY *pkey, PKCS8_PRIV_KEY_INFO *p8)
     STACK_OF(ASN1_TYPE) *ndsa = NULL;
     DSA *dsa = NULL;
 
+    int ret = 0;
+
     if (!PKCS8_pkey_get0(NULL, &p, &pklen, &palg, p8))
         return 0;
     X509_ALGOR_get0(NULL, &ptype, &pval, palg);
@@ -262,23 +264,21 @@ static int dsa_priv_decode(EVP_PKEY *pkey, PKCS8_PRIV_KEY_INFO *p8)
     }
 
     EVP_PKEY_assign_DSA(pkey, dsa);
-    BN_CTX_free(ctx);
-    if (ndsa)
-        sk_ASN1_TYPE_pop_free(ndsa, ASN1_TYPE_free);
-    else
-        ASN1_STRING_clear_free(privkey);
 
-    return 1;
+    ret = 1;
+    goto done;
 
  decerr:
     DSAerr(DSA_F_DSA_PRIV_DECODE, DSA_R_DECODE_ERROR);
  dsaerr:
+    DSA_free(dsa);
+ done:
     BN_CTX_free(ctx);
-    if (privkey)
+    if (ndsa)
+        sk_ASN1_TYPE_pop_free(ndsa, ASN1_TYPE_free);
+    else
         ASN1_STRING_clear_free(privkey);
-    sk_ASN1_TYPE_pop_free(ndsa, ASN1_TYPE_free);
-    DSA_free(dsa);
-    return 0;
+    return ret;
 }
 
 static int dsa_priv_encode(PKCS8_PRIV_KEY_INFO *p8, const EVP_PKEY *pkey)