PKCS#7: Better handling of unsupported crypto

Provide better handling of unsupported crypto when verifying a PKCS#7 message.
If we can't bridge the gap between a pair of X.509 certs or between a signed
info block and an X.509 cert because it involves some crypto we don't support,
that's not necessarily the end of the world as there may be other ways points
at which we can intersect with a ring of trusted keys.

Instead, only produce ENOPKG immediately if all the signed info blocks in a
PKCS#7 message require unsupported crypto to bridge to the first X.509 cert.
Otherwise, we defer the generation of ENOPKG until we get ENOKEY during trust
validation.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

1 files changed, 19 insertions, 10 deletions

diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
index 09197e5..8bd474e 100644
--- a/crypto/asymmetric_keys/pkcs7_trust.c
+++ b/crypto/asymmetric_keys/pkcs7_trust.c
@@ -35,6 +35,11 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
 
 	kenter(",%u,", sinfo->index);
 
+	if (sinfo->unsupported_crypto) {
+		kleave(" = -ENOPKG [cached]");
+		return -ENOPKG;
+	}
+
 	for (x509 = sinfo->signer; x509; x509 = x509->signer) {
 		if (x509->seen) {
 			if (x509->verified) {
@@ -139,24 +144,28 @@ int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
 {
 	struct pkcs7_signed_info *sinfo;
 	struct x509_certificate *p;
-	int cached_ret = 0, ret;
+	int cached_ret = -ENOKEY;
+	int ret;
 
 	for (p = pkcs7->certs; p; p = p->next)
 		p->seen = false;
 
 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
 		ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
-		if (ret < 0) {
-			if (ret == -ENOPKG) {
+		switch (ret) {
+		case -ENOKEY:
+			continue;
+		case -ENOPKG:
+			if (cached_ret == -ENOKEY)
 				cached_ret = -ENOPKG;
-			} else if (ret == -ENOKEY) {
-				if (cached_ret == 0)
-					cached_ret = -ENOKEY;
-			} else {
-				return ret;
-			}
+			continue;
+		case 0:
+			*_trusted |= sinfo->trusted;
+			cached_ret = 0;
+			continue;
+		default:
+			return ret;
 		}
-		*_trusted |= sinfo->trusted;
 	}
 
 	return cached_ret;