[PATCH 3/3] x509: add CRL signature verification support

Verify the digital signature of Certificate Revocation Lists (CRLs)
before processing their entries.  Extract signature parameters via
x509_get_sig_params() and preserve the TBS data during parsing to
enable signature verification with verify_signature().

Add the keyring parameter to x509_load_crl_list() to specify which
keyring to use for CRL issuer lookup.  If no keyring is provided,
signature verification is skipped.

Signed-off-by: Timofei Novikov <[email protected]>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 11 ++++++++
 crypto/asymmetric_keys/x509_crl.asn1      |  2 +-
 crypto/asymmetric_keys/x509_loader.c      | 31 ++++++++++++++++++++++-
 crypto/asymmetric_keys/x509_parser.h      |  2 +-
 include/keys/asymmetric-type.h            |  3 ++-
 5 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 76b61f36c082..39ef4cf4b05d 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -907,14 +907,24 @@ struct x509_crl_context *x509_crl_parse(const void *data, size_t datalen)
 	if (ret < 0)
 		return ERR_PTR(ret);
 
+	/*
+	 * Extract signature parameters (sig->s, sig->digest, etc.)
+	 * This does what we previously tried to do manually.
+	 */
+	ret = x509_get_sig_params(cert);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
 	/* Transfer parsed data to crl_context */
 	INIT_LIST_HEAD(&crl_ctx->revoked_list);
 	crl_ctx->indirect_crl = ctx->indirect_crl;
 	crl_ctx->raw_issuer = cert->raw_issuer;
 	crl_ctx->raw_issuer_size = cert->raw_issuer_size;
+	crl_ctx->sig = cert->sig;
 	list_splice(&ctx->revoked_list, &crl_ctx->revoked_list);
 
 	/* Detach pointers from cert before auto-free */
+	cert->sig = NULL;
 	cert->raw_issuer = NULL;
 	cert->raw_serial = NULL;
 
@@ -930,6 +940,7 @@ void x509_crl_free(struct x509_crl_context *ctx)
 		kfree(entry->serial);
 		kfree(entry);
 	}
+	public_key_signature_free(ctx->sig);
 	kfree(ctx);
 }
 
diff --git a/crypto/asymmetric_keys/x509_crl.asn1 b/crypto/asymmetric_keys/x509_crl.asn1
index 3ec8f5a32aca..910af624d828 100644
--- a/crypto/asymmetric_keys/x509_crl.asn1
+++ b/crypto/asymmetric_keys/x509_crl.asn1
@@ -16,7 +16,7 @@ TBSCertList ::= SEQUENCE {
 	nextUpdate		Time OPTIONAL ({ x509_note_not_after }) ,
 	revokedCertificates	SEQUENCE OF RevokedCertificate OPTIONAL,
 	crlExtensions		[ 0 ] Extensions OPTIONAL
-	}
+	} ({ x509_note_tbs_certificate })
 
 RevokedCertificate ::= SEQUENCE {
 	userCertificate		CertificateSerialNumber ({ crl_note_serial }),
diff --git a/crypto/asymmetric_keys/x509_loader.c b/crypto/asymmetric_keys/x509_loader.c
index 344e6bf31612..7c1a098b2ecb 100644
--- a/crypto/asymmetric_keys/x509_loader.c
+++ b/crypto/asymmetric_keys/x509_loader.c
@@ -6,6 +6,7 @@
 #include <keys/system_keyring.h>
 #include <linux/slab.h>
 #include <crypto/sha2.h>
+#include <crypto/public_key.h>
 #include "x509_parser.h"
 
 int x509_load_certificate_list(const u8 cert_list[],
@@ -74,7 +75,30 @@ static const void *crl_entry_issuer(const struct x509_crl_context *crl,
 	return crl->raw_issuer;
 }
 
-int x509_load_crl_list(const u8 crl_list[], const unsigned long list_size)
+static int x509_crl_verify_signature(struct x509_crl_context *crl_ctx,
+				     const struct key *keyring)
+{
+	struct key *key;
+	int ret = -ENOKEY;
+
+	if (!crl_ctx->raw_issuer || !crl_ctx->sig)
+		return -ENOKEY;
+
+	key = find_asymmetric_key(keyring,
+				  crl_ctx->sig->auth_ids[0],
+				  crl_ctx->sig->auth_ids[1],
+				  crl_ctx->sig->auth_ids[2],
+				  false);
+	if (IS_ERR(key))
+		return PTR_ERR(key);
+
+	ret = verify_signature(key, crl_ctx->sig);
+	key_put(key);
+	return ret;
+}
+
+int x509_load_crl_list(const u8 crl_list[], const unsigned long list_size,
+		       const struct key *keyring)
 {
 	const u8 *p = crl_list, *end = p + list_size;
 
@@ -107,6 +131,11 @@ int x509_load_crl_list(const u8 crl_list[], const unsigned long list_size)
 			pr_err("Problem parsing CRL (%ld)\n", PTR_ERR(crl_ctx));
 			goto next_crl;
 		}
+		if (keyring && x509_crl_verify_signature(crl_ctx, keyring) < 0) {
+			pr_warn("CRL signature verification failed, skipping\n");
+			x509_crl_free(crl_ctx);
+			goto next_crl;
+		}
 		list_for_each_entry_safe(entry, tmp, &crl_ctx->revoked_list, list) {
 			struct asymmetric_key_id *kid;
 			const void *issuer;
diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
index 13cc0bc3d7e2..7c48ccb1008c 100644
--- a/crypto/asymmetric_keys/x509_parser.h
+++ b/crypto/asymmetric_keys/x509_parser.h
@@ -49,9 +49,9 @@ struct x509_certificate {
 struct x509_crl_context {
 	const void *raw_issuer;
 	size_t raw_issuer_size;
+	struct public_key_signature *sig;
 	struct list_head revoked_list;
 	bool indirect_crl;
-	u8 crl_reason;
 };
 
 struct x509_revoked_entry {
diff --git a/include/keys/asymmetric-type.h b/include/keys/asymmetric-type.h
index 635644c8dcf1..db586a4c2981 100644
--- a/include/keys/asymmetric-type.h
+++ b/include/keys/asymmetric-type.h
@@ -87,7 +87,8 @@ extern struct key *find_asymmetric_key(struct key *keyring,
 int x509_load_certificate_list(const u8 cert_list[], const unsigned long list_size,
 			       const struct key *keyring);
 #ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
-int x509_load_crl_list(const u8 crl_list[], const unsigned long list_size);
+int x509_load_crl_list(const u8 crl_list[], const unsigned long list_size,
+		       const struct key *keyring);
 #endif
 
 /*
-- 
2.43.0