[PATCH] KEYS: Make use of platform keyring for module signature verification

[Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx>]

This allows a cert in DB to be used to sign modules,
in addition to certs in the MoK and built-in keyrings.

This key policy matches what's used for kexec.

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx>
---

Notes:
    Debian has carried an equivalent patch since 5.3.9-1:
      https://bugs.debian.org/935945
      https://bugs.debian.org/1030200
    in
      https://salsa.debian.org/kernel-team/linux/-/commit/0e65c8f3e316d6f0fc30f091dd47dba2ac616529
    and it appears the true origin is some version of
      https://gitlab.com/cki-project/kernel-ark/-/commit/b697ff5e26974fee8fcd31a1e221e9dd41515efc

 kernel/module/signing.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/module/signing.c b/kernel/module/signing.c
index a2ff4242e623..71d6248cf9ec 100644
--- a/kernel/module/signing.c
+++ b/kernel/module/signing.c
@@ -61,10 +61,16 @@ int mod_verify_sig(const void *mod, struct load_info *info)
 	modlen -= sig_len + sizeof(ms);
 	info->len = modlen;
 
-	return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
-				      VERIFY_USE_SECONDARY_KEYRING,
-				      VERIFYING_MODULE_SIGNATURE,
-				      NULL, NULL);
+	ret = verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
+				     VERIFY_USE_SECONDARY_KEYRING,
+				     VERIFYING_MODULE_SIGNATURE,
+				     NULL, NULL);
+	if (ret == -ENOKEY && IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING))
+		ret = verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
+					     VERIFY_USE_PLATFORM_KEYRING,
+					     VERIFYING_MODULE_SIGNATURE,
+					     NULL, NULL);
+	return ret;
 }
 
 int module_sig_check(struct load_info *info, int flags)
-- 
2.30.2

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