PKCS#7: Verify internal certificate chain

Verify certificate chain in the X.509 certificates contained within the PKCS#7
message as far as possible.  If any signature that we should be able to verify
fails, we reject the whole lot.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

1 files changed, 87 insertions, 1 deletions

diff --git a/crypto/asymmetric_keys/pkcs7_verify.c b/crypto/asymmetric_keys/pkcs7_verify.c
index 745e5c86a35e..51ff36f3a913 100644
--- a/crypto/asymmetric_keys/pkcs7_verify.c
+++ b/crypto/asymmetric_keys/pkcs7_verify.c
@@ -170,6 +170,91 @@ static int pkcs7_find_key(struct pkcs7_message *pkcs7,
 }
 
 /*
+ * Verify the internal certificate chain as best we can.
+ */
+static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
+                                  struct pkcs7_signed_info *sinfo)
+{
+        struct x509_certificate *x509 = sinfo->signer, *p;
+        int ret;
+
+        kenter("");
+
+        for (p = pkcs7->certs; p; p = p->next)
+                p->seen = false;
+
+        for (;;) {
+                pr_debug("verify %s: %s\n", x509->subject, x509->fingerprint);
+                x509->seen = true;
+                ret = x509_get_sig_params(x509);
+                if (ret < 0)
+                        return ret;
+
+                if (x509->issuer)
+                        pr_debug("- issuer %s\n", x509->issuer);
+                if (x509->authority)
+                        pr_debug("- authkeyid %s\n", x509->authority);
+
+                if (!x509->authority ||
+                    (x509->subject &&
+                     strcmp(x509->subject, x509->issuer) == 0)) {
+                        /* If there's no authority certificate specified, then
+                         * the certificate must be self-signed and is the root
+                         * of the chain.  Likewise if the cert is its own
+                         * authority.
+                         */
+                        pr_debug("- no auth?\n");
+                        if (x509->raw_subject_size != x509->raw_issuer_size ||
+                            memcmp(x509->raw_subject, x509->raw_issuer,
+                                   x509->raw_issuer_size) != 0)
+                                return 0;
+
+                        ret = x509_check_signature(x509->pub, x509);
+                        if (ret < 0)
+                                return ret;
+                        x509->signer = x509;
+                        pr_debug("- self-signed\n");
+                        return 0;
+                }
+
+                /* Look through the X.509 certificates in the PKCS#7 message's
+                 * list to see if the next one is there.
+                 */
+                pr_debug("- want %s\n", x509->authority);
+                for (p = pkcs7->certs; p; p = p->next) {
+                        pr_debug("- cmp [%u] %s\n", p->index, p->fingerprint);
+                        if (p->raw_subject_size == x509->raw_issuer_size &&
+                            strcmp(p->fingerprint, x509->authority) == 0 &&
+                            memcmp(p->raw_subject, x509->raw_issuer,
+                                   x509->raw_issuer_size) == 0)
+                                goto found_issuer;
+                }
+
+                /* We didn't find the root of this chain */
+                pr_debug("- top\n");
+                return 0;
+
+        found_issuer:
+                pr_debug("- issuer %s\n", p->subject);
+                if (p->seen) {
+                        pr_warn("Sig %u: X.509 chain contains loop\n",
+                                sinfo->index);
+                        return 0;
+                }
+                ret = x509_check_signature(p->pub, x509);
+                if (ret < 0)
+                        return ret;
+                x509->signer = p;
+                if (x509 == p) {
+                        pr_debug("- self-signed\n");
+                        return 0;
+                }
+                x509 = p;
+                might_sleep();
+        }
+}
+
+/*
  * Verify one signed information block from a PKCS#7 message.
  */
 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
@@ -201,7 +286,8 @@ static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
 
         pr_devel("Verified signature %u\n", sinfo->index);
 
-        return 0;
+        /* Verify the internal certificate chain */
+        return pkcs7_verify_sig_chain(pkcs7, sinfo);
 }
 
 /**