[PATCH v1 4/9] certs: Check that builtin blacklist hashes are valid

Mickaël Salaün mic at digikod.net
Fri Nov 20 18:04:21 UTC 2020


From: Mickaël Salaün <mic at linux.microsoft.com>

Add and use a check-blacklist-hashes.awk script to make sure that the
builtin blacklist hashes will be approved by the run time blacklist
description checks.  This is useful to debug invalid hash formats, and
it make sure that previous hashes which could have been loaded in the
kernel (but ignored) are now noticed and deal with by the user.

Cc: David Howells <dhowells at redhat.com>
Cc: David Woodhouse <dwmw2 at infradead.org>
Signed-off-by: Mickaël Salaün <mic at linux.microsoft.com>
---
 MAINTAINERS                        |  1 +
 certs/.gitignore                   |  1 +
 certs/Makefile                     | 15 +++++++++++-
 scripts/check-blacklist-hashes.awk | 37 ++++++++++++++++++++++++++++++
 4 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100755 scripts/check-blacklist-hashes.awk

diff --git a/MAINTAINERS b/MAINTAINERS
index e451dcce054f..a5b0c59f55a0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4090,6 +4090,7 @@ L:	keyrings at vger.kernel.org
 S:	Maintained
 F:	Documentation/admin-guide/module-signing.rst
 F:	certs/
+F:	scripts/check-blacklist-hashes.awk
 F:	scripts/extract-cert.c
 F:	scripts/sign-file.c
 
diff --git a/certs/.gitignore b/certs/.gitignore
index 2a2483990686..42cc2ac24b93 100644
--- a/certs/.gitignore
+++ b/certs/.gitignore
@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
+blacklist_hashes_checked
 x509_certificate_list
diff --git a/certs/Makefile b/certs/Makefile
index f4c25b67aad9..36d45b85e069 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -6,7 +6,20 @@
 obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist.o
 ifneq ($(CONFIG_SYSTEM_BLACKLIST_HASH_LIST),"")
+
+quiet_cmd_check_blacklist_hashes = CHECK   $(patsubst "%",%,$(2))
+      cmd_check_blacklist_hashes = $(AWK) -f scripts/check-blacklist-hashes.awk $(2); touch $@
+
+$(eval $(call config_filename,SYSTEM_BLACKLIST_HASH_LIST))
+
+$(obj)/blacklist_hashes.o: $(obj)/blacklist_hashes_checked
+
+targets += blacklist_hashes_checked
+$(obj)/blacklist_hashes_checked: $(SYSTEM_BLACKLIST_HASH_LIST_SRCPREFIX)$(SYSTEM_BLACKLIST_HASH_LIST_FILENAME) scripts/check-blacklist-hashes.awk FORCE
+	$(call if_changed,check_blacklist_hashes,$(SYSTEM_BLACKLIST_HASH_LIST_SRCPREFIX)$(CONFIG_SYSTEM_BLACKLIST_HASH_LIST))
+
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_hashes.o
+
 else
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_nohashes.o
 endif
@@ -29,7 +42,7 @@ $(obj)/x509_certificate_list: scripts/extract-cert $(SYSTEM_TRUSTED_KEYS_SRCPREF
 	$(call if_changed,extract_certs,$(SYSTEM_TRUSTED_KEYS_SRCPREFIX)$(CONFIG_SYSTEM_TRUSTED_KEYS))
 endif # CONFIG_SYSTEM_TRUSTED_KEYRING
 
-clean-files := x509_certificate_list .x509.list
+clean-files := x509_certificate_list .x509.list blacklist_hashes_checked
 
 ifeq ($(CONFIG_MODULE_SIG),y)
 ###############################################################################
diff --git a/scripts/check-blacklist-hashes.awk b/scripts/check-blacklist-hashes.awk
new file mode 100755
index 000000000000..4d3c676b7aef
--- /dev/null
+++ b/scripts/check-blacklist-hashes.awk
@@ -0,0 +1,37 @@
+#!/usr/bin/awk -f
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright © 2020, Microsoft Corporation. All rights reserved.
+#
+# Author: Mickaël Salaün <mic at linux.microsoft.com>
+#
+# Check that a CONFIG_SYSTEM_BLACKLIST_HASH_LIST file contains a valid array of
+# hash strings.  Such string must start with a prefix ("tbs" or "bin"), then a
+# colon (":"), and finally an even number of hexadecimal lowercase characters
+# (up to 128).
+
+BEGIN {
+	RS = ","
+}
+{
+	if (!match($0, "^[ \t\n\r]*\"([^\"]*)\"[ \t\n\r]*$", part1)) {
+		print "Not a string (item " NR "):", $0;
+		exit 1;
+	}
+	if (!match(part1[1], "^(tbs|bin):(.*)$", part2)) {
+		print "Unknown prefix (item " NR "):", part1[1];
+		exit 1;
+	}
+	if (!match(part2[2], "^([0-9a-z]+)$", part3)) {
+		print "Not a lowercase hexadecimal string (item " NR "):", part2[2];
+		exit 1;
+	}
+	if (length(part3[1]) > 128) {
+		print "Hash string too long (item " NR "):", part3[1];
+		exit 1;
+	}
+	if (length(part3[1]) % 2 == 1) {
+		print "Not an even number of hexadecimal characters (item " NR "):", part3[1];
+		exit 1;
+	}
+}
-- 
2.29.2



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