From a9643aef5a6c576f32a97053b4024638943044ca Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Wed, 5 Apr 2017 17:40:30 +0100
Subject: [PATCH 42/62] Enforce module signatures if the kernel is locked down
Patch-mainline: No, submitted https://patchwork.kernel.org/patch/9664927/
References: fate#314486

If the kernel is locked down, require that all modules have valid
signatures that we can verify.


[ modified according to this proposed change: https://lkml.org/lkml/2018/2/22/359 ]

It adjusts the errors generated:

 (1) If there's no signature (ENODATA) or we can't check it (ENOPKG, ENOKEY),
     then:

     (a) If signatures are enforced then EKEYREJECTED is returned.

     (b) If IMA will have validated the image, return 0 (okay).

     (c) If there's no signature or we can't check it, but the kernel is
	 locked down then EPERM is returned (this is then consistent with
	 other lockdown cases).

 (2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails
     the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we return
     the error we got.

Note that the X.509 code doesn't check for key expiry as the RTC might not be
valid or might not have been transferred to the kernel's clock yet.


Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jiri Bohac <jbohac@suse.cz>
---
---
 kernel/module.c |   41 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2824,8 +2824,9 @@ static inline void kmemleak_load_module(
 #ifdef CONFIG_MODULE_SIG
 static int module_sig_check(struct load_info *info, int flags)
 {
-	int err = -ENOKEY;
+	int err = -ENODATA;
 	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
+	const char *reason;
 	const void *mod = info->hdr;
 
 	/*
@@ -2840,16 +2841,42 @@ static int module_sig_check(struct load_
 		err = mod_verify_sig(mod, info);
 	}
 
-	if (!err) {
+	switch (err) {
+	case 0:
 		info->sig_ok = true;
 		return 0;
-	}
 
-	/* Not having a signature is only an error if we're strict. */
-	if (err == -ENOKEY && !sig_enforce)
-		err = 0;
+		/* We don't permit modules to be loaded into trusted kernels
+		 * without a valid signature on them, but if we're not
+		 * enforcing, certain errors are non-fatal.
+		 */
+	case -ENODATA:
+		reason = "Loading of unsigned module";
+		goto decide;
+	case -ENOPKG:
+		reason = "Loading of module with unsupported crypto";
+		goto decide;
+	case -ENOKEY:
+		reason = "Loading of module with unavailable key";
+	decide:
+		if (sig_enforce) {
+			pr_notice("%s is rejected\n", reason);
+			return -EKEYREJECTED;
+		}
+		if (kernel_is_locked_down()) {
+			pr_notice("%s is rejected, kernel is locked down\n", reason);
+			return -EPERM;
+		}
+		return 0;
+
+		/* All other errors are fatal, including nomem, unparseable
+		 * signatures and signature check failures - even if signatures
+		 * aren't required.
+		 */
+	default:
+		return err;
+	}
 
-	return err;
 }
 #else /* !CONFIG_MODULE_SIG */
 static int module_sig_check(struct load_info *info, int flags)