Fix a padding oracle in PKCS7_dataDecode and CMS_decrypt_set1_pkey.

(Note that the CMS code is currently disabled.)

Port of Edlinger's Fix for CVE-2019-1563 from OpenSSL 1.1.1 (old license)

tests from bluhm@
ok jsing

commit e21f8cf78a125cd3c8c0d1a1a6c8bb0b901f893f
Author: Bernd Edlinger <bernd.edlinger@hotmail.de>
Date:   Sun Sep 1 00:16:28 2019 +0200

    Fix a padding oracle in PKCS7_dataDecode and CMS_decrypt_set1_pkey

    An attack is simple, if the first CMS_recipientInfo is valid but the
    second CMS_recipientInfo is chosen ciphertext. If the second
    recipientInfo decodes to PKCS #1 v1.5 form plaintext, the correct
    encryption key will be replaced by garbage, and the message cannot be
    decoded, but if the RSA decryption fails, the correct encryption key is
    used and the recipient will not notice the attack.

    As a work around for this potential attack the length of the decrypted
    key must be equal to the cipher default key length, in case the
    certifiate is not given and all recipientInfo are tried out.

    The old behaviour can be re-enabled in the CMS code by setting the
    CMS_DEBUG_DECRYPT flag.

    Reviewed-by: Matt Caswell <matt@openssl.org>
    (Merged from https://github.com/openssl/openssl/pull/9777)

    (cherry picked from commit 5840ed0cd1e6487d247efbc1a04136a41d7b3a37)

1 files changed, 8 insertions, 7 deletions

diff --git a/src/lib/libcrypto/pkcs7/pk7_doit.c b/src/lib/libcrypto/pkcs7/pk7_doit.c
index d0c27e98a9..81a72f6815 100644
--- a/src/lib/libcrypto/pkcs7/pk7_doit.c
+++ b/src/lib/libcrypto/pkcs7/pk7_doit.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: pk7_doit.c,v 1.43 2019/03/13 20:34:00 tb Exp $ */
+/* $OpenBSD: pk7_doit.c,v 1.44 2019/10/04 18:03:55 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -191,7 +191,7 @@ err:
 
 static int
 pkcs7_decrypt_rinfo(unsigned char **pek, int *peklen, PKCS7_RECIP_INFO *ri,
-    EVP_PKEY *pkey)
+    EVP_PKEY *pkey, size_t fixlen)
 {
         EVP_PKEY_CTX *pctx = NULL;
         unsigned char *ek = NULL;
@@ -222,8 +222,9 @@ pkcs7_decrypt_rinfo(unsigned char **pek, int *peklen, PKCS7_RECIP_INFO *ri,
                 goto err;
         }
 
-        if (EVP_PKEY_decrypt(pctx, ek, &eklen,
-            ri->enc_key->data, ri->enc_key->length) <= 0) {
+        if (EVP_PKEY_decrypt(pctx, ek, &eklen, ri->enc_key->data,
+            ri->enc_key->length) <= 0 || eklen == 0 ||
+            (fixlen != 0 && eklen != fixlen)) {
                 ret = 0;
                 PKCS7error(ERR_R_EVP_LIB);
                 goto err;
@@ -535,14 +536,14 @@ PKCS7_dataDecode(PKCS7 *p7, EVP_PKEY *pkey, BIO *in_bio, X509 *pcert)
                         for (i = 0; i < sk_PKCS7_RECIP_INFO_num(rsk); i++) {
                                 ri = sk_PKCS7_RECIP_INFO_value(rsk, i);
 
-                                if (pkcs7_decrypt_rinfo(&ek, &eklen,
-                                    ri, pkey) < 0)
+                                if (pkcs7_decrypt_rinfo(&ek, &eklen, ri, pkey,
+                                    EVP_CIPHER_key_length(evp_cipher)) < 0)
                                         goto err;
                                 ERR_clear_error();
                         }
                 } else {
                         /* Only exit on fatal errors, not decrypt failure */
-                        if (pkcs7_decrypt_rinfo(&ek, &eklen, ri, pkey) < 0)
+                        if (pkcs7_decrypt_rinfo(&ek, &eklen, ri, pkey, 0) < 0)
                                 goto err;
                         ERR_clear_error();
                 }