From 091f6e26eb326adbd718f406e440c838bed8ebb6 Mon Sep 17 00:00:00 2001
From: David Howells
Date: Mon, 20 Jul 2015 21:16:28 +0100
Subject: MODSIGN: Extract the blob PKCS#7 signature verifier from module
 signing

Extract the function that drives the PKCS#7 signature verification given a
data blob and a PKCS#7 blob out from the module signing code and lump it with
the system keyring code as it's generic.  This makes it independent of module
config options and opens it to use by the firmware loader.

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ming Lei <ming.lei@canonical.com>
Cc: Seth Forshee <seth.forshee@canonical.com>
Cc: Kyle McMartin <kyle@kernel.org>
---
 kernel/system_keyring.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

(limited to 'kernel/system_keyring.c')

diff --git a/kernel/system_keyring.c b/kernel/system_keyring.c
index 4cda71ee51c7..95f2dcbc7616 100644
--- a/kernel/system_keyring.c
+++ b/kernel/system_keyring.c
@@ -16,6 +16,7 @@
 #include <linux/err.h>
 #include <keys/asymmetric-type.h>
 #include <keys/system_keyring.h>
+#include <crypto/pkcs7.h>
 
 struct key *system_trusted_keyring;
 EXPORT_SYMBOL_GPL(system_trusted_keyring);
@@ -103,3 +104,52 @@ dodgy_cert:
 	return 0;
 }
 late_initcall(load_system_certificate_list);
+
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+
+/**
+ * Verify a PKCS#7-based signature on system data.
+ * @data: The data to be verified.
+ * @len: Size of @data.
+ * @raw_pkcs7: The PKCS#7 message that is the signature.
+ * @pkcs7_len: The size of @raw_pkcs7.
+ */
+int system_verify_data(const void *data, unsigned long len,
+		       const void *raw_pkcs7, size_t pkcs7_len)
+{
+	struct pkcs7_message *pkcs7;
+	bool trusted;
+	int ret;
+
+	pkcs7 = pkcs7_parse_message(raw_pkcs7, pkcs7_len);
+	if (IS_ERR(pkcs7))
+		return PTR_ERR(pkcs7);
+
+	/* The data should be detached - so we need to supply it. */
+	if (pkcs7_supply_detached_data(pkcs7, data, len) < 0) {
+		pr_err("PKCS#7 signature with non-detached data\n");
+		ret = -EBADMSG;
+		goto error;
+	}
+
+	ret = pkcs7_verify(pkcs7);
+	if (ret < 0)
+		goto error;
+
+	ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, &trusted);
+	if (ret < 0)
+		goto error;
+
+	if (!trusted) {
+		pr_err("PKCS#7 signature not signed with a trusted key\n");
+		ret = -ENOKEY;
+	}
+
+error:
+	pkcs7_free_message(pkcs7);
+	pr_devel("<==%s() = %d\n", __func__, ret);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(system_verify_data);
+
+#endif /* CONFIG_SYSTEM_DATA_VERIFICATION */
-- 
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