From 6459ae386699a5fe0dc52cf30255f75274fa43a4 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Thu, 22 Feb 2018 14:38:33 +0000
Subject: [PATCH] PKCS#7: fix direct verification of SignerInfo signature
Git-commit: 6459ae386699a5fe0dc52cf30255f75274fa43a4
Patch-mainline: v4.16-rc3
References: bsc#1051510

If none of the certificates in a SignerInfo's certificate chain match a
trusted key, nor is the last certificate signed by a trusted key, then
pkcs7_validate_trust_one() tries to check whether the SignerInfo's
signature was made directly by a trusted key.  But, it actually fails to
set the 'sig' variable correctly, so it actually verifies the last
signature seen.  That will only be the SignerInfo's signature if the
certificate chain is empty; otherwise it will actually be the last
certificate's signature.

This is not by itself a security problem, since verifying any of the
certificates in the chain should be sufficient to verify the SignerInfo.
Still, it's not working as intended so it should be fixed.

Fix it by setting 'sig' correctly for the direct verification case.

Fixes: 757932e6da6d ("PKCS#7: Handle PKCS#7 messages that contain no X.509 certs")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 crypto/asymmetric_keys/pkcs7_trust.c |    1 +
 1 file changed, 1 insertion(+)

--- a/crypto/asymmetric_keys/pkcs7_trust.c
+++ b/crypto/asymmetric_keys/pkcs7_trust.c
@@ -106,6 +106,7 @@ static int pkcs7_validate_trust_one(stru
 		pr_devel("sinfo %u: Direct signer is key %x\n",
 			 sinfo->index, key_serial(key));
 		x509 = NULL;
+		sig = sinfo->sig;
 		goto matched;
 	}
 	if (PTR_ERR(key) != -ENOKEY)