PKCS#7: fix direct verification of SignerInfo signature

ebiggers · dhowells · commit 6459ae386699 · 2018-02-22T14:38:33.000Z
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: 757932e ("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>
diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
@@ -106,6 +106,7 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 		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)

Original file line number	Diff line number	Diff line change
`@@ -106,6 +106,7 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,`
`106`	`106`	`pr_devel("sinfo %u: Direct signer is key %x\n",`
`107`	`107`	`sinfo->index, key_serial(key));`
`108`	`108`	`x509 = NULL;`
	`109`	`+ sig = sinfo->sig;`
`109`	`110`	`goto matched;`
`110`	`111`	`}`
`111`	`112`	`if (PTR_ERR(key) != -ENOKEY)`