diff mbox series

[v3,08/10] certs: Check that builtin blacklist hashes are valid

Message ID 20210114151909.2344974-9-mic@digikod.net (mailing list archive)
State New, archived
Headers show
Series Enable root to update the blacklist keyring | expand

Commit Message

Mickaël Salaün Jan. 14, 2021, 3:19 p.m. UTC 
From: Mickaël Salaün <mic@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@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
---

Changes since v2:
* Add Jarkko's Acked-by.

Changes since v1:
* Prefix script path with $(scrtree)/ (suggested by David Howells).
* Fix hexadecimal number check.
---
 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

Comments

Jarkko Sakkinen Jan. 20, 2021, 5:19 a.m. UTC | #1 
On Thu, Jan 14, 2021 at 04:19:07PM +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@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@redhat.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
> Acked-by: Jarkko Sakkinen <jarkko@kernel.org>

I get this with a self-signed cert:

certs/Makefile:18: *** target pattern contains no '%'.  Stop.

CONFIG_SYSTEM_BLACKLIST_HASH_LIST="tbs:8eed1340eef37c1dc84d996406ad05c7dbb3eade19132d688408ca2f63904869"

I used the script in 10/10 to test this, which is another
reamark: the patches are in invalid order, as you need to
apply 10/10 before you can test  8/10.

/Jarkko
Mickaël Salaün Jan. 20, 2021, 11:57 a.m. UTC | #2 
On 20/01/2021 06:19, Jarkko Sakkinen wrote:
> On Thu, Jan 14, 2021 at 04:19:07PM +0100, Mickaël Salaün wrote:
>> From: Mickaël Salaün <mic@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@redhat.com>
>> Cc: David Woodhouse <dwmw2@infradead.org>
>> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
>> Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
> 
> I get this with a self-signed cert:
> 
> certs/Makefile:18: *** target pattern contains no '%'.  Stop.
> 
> CONFIG_SYSTEM_BLACKLIST_HASH_LIST="tbs:8eed1340eef37c1dc84d996406ad05c7dbb3eade19132d688408ca2f63904869"

As said in the Kconfig documentation for
CONFIG_SYSTEM_BLACKLIST_HASH_LIST, you need to provide a file with the
list, not to set the string directly in the configuration variable. This
patch series didn't change this behavior. The same kind of macros are
used for CONFIG_MODULE_SIG_KEY.

> 
> I used the script in 10/10 to test this, which is another
> reamark: the patches are in invalid order, as you need to
> apply 10/10 before you can test  8/10.

I'll move patch 10/10 earlier but this kind of formatting was already
required (but silently ignored) for this option to be really taken into
account. Only the kernel code was available to understand how to
effectively create such hash.

> 
> /Jarkko
>
Jarkko Sakkinen Jan. 20, 2021, 11:53 p.m. UTC | #3 
On Wed, Jan 20, 2021 at 12:57:55PM +0100, Mickaël Salaün wrote:
> 
> On 20/01/2021 06:19, Jarkko Sakkinen wrote:
> > On Thu, Jan 14, 2021 at 04:19:07PM +0100, Mickaël Salaün wrote:
> >> From: Mickaël Salaün <mic@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@redhat.com>
> >> Cc: David Woodhouse <dwmw2@infradead.org>
> >> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
> >> Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
> > 
> > I get this with a self-signed cert:
> > 
> > certs/Makefile:18: *** target pattern contains no '%'.  Stop.
> > 
> > CONFIG_SYSTEM_BLACKLIST_HASH_LIST="tbs:8eed1340eef37c1dc84d996406ad05c7dbb3eade19132d688408ca2f63904869"
> 
> As said in the Kconfig documentation for
> CONFIG_SYSTEM_BLACKLIST_HASH_LIST, you need to provide a file with the
> list, not to set the string directly in the configuration variable. This
> patch series didn't change this behavior. The same kind of macros are
> used for CONFIG_MODULE_SIG_KEY.

OK, the documentation just states that:

"Hashes to be preloaded into the system blacklist keyring"

No mention about a file. I'd add a patch to update this documentation.

> 
> > 
> > I used the script in 10/10 to test this, which is another
> > reamark: the patches are in invalid order, as you need to
> > apply 10/10 before you can test  8/10.
> 
> I'll move patch 10/10 earlier but this kind of formatting was already
> required (but silently ignored) for this option to be really taken into
> account. Only the kernel code was available to understand how to
> effectively create such hash.

Great, thanks.


> > 
> > /Jarkko
> > 


/Jarkko
Mickaël Salaün Jan. 21, 2021, 9:18 a.m. UTC | #4 
On 21/01/2021 00:53, Jarkko Sakkinen wrote:
> On Wed, Jan 20, 2021 at 12:57:55PM +0100, Mickaël Salaün wrote:
>>
>> On 20/01/2021 06:19, Jarkko Sakkinen wrote:
>>> On Thu, Jan 14, 2021 at 04:19:07PM +0100, Mickaël Salaün wrote:
>>>> From: Mickaël Salaün <mic@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@redhat.com>
>>>> Cc: David Woodhouse <dwmw2@infradead.org>
>>>> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
>>>> Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
>>>
>>> I get this with a self-signed cert:
>>>
>>> certs/Makefile:18: *** target pattern contains no '%'.  Stop.
>>>
>>> CONFIG_SYSTEM_BLACKLIST_HASH_LIST="tbs:8eed1340eef37c1dc84d996406ad05c7dbb3eade19132d688408ca2f63904869"
>>
>> As said in the Kconfig documentation for
>> CONFIG_SYSTEM_BLACKLIST_HASH_LIST, you need to provide a file with the
>> list, not to set the string directly in the configuration variable. This
>> patch series didn't change this behavior. The same kind of macros are
>> used for CONFIG_MODULE_SIG_KEY.
> 
> OK, the documentation just states that:
> 
> "Hashes to be preloaded into the system blacklist keyring"
> 
> No mention about a file. I'd add a patch to update this documentation.

I was referring to the full description:

config SYSTEM_BLACKLIST_HASH_LIST
	string "Hashes to be preloaded into the system blacklist keyring"
	depends on SYSTEM_BLACKLIST_KEYRING
	help
	  If set, this option should be the filename of a list of hashes in the
	  form "<hash>", "<hash>", ... .  This will be included into a C
	  wrapper to incorporate the list into the kernel.  Each <hash> should
	  be a string of hex digits.

…but the short description doesn't mention filename.

> 
>>
>>>
>>> I used the script in 10/10 to test this, which is another
>>> reamark: the patches are in invalid order, as you need to
>>> apply 10/10 before you can test  8/10.
>>
>> I'll move patch 10/10 earlier but this kind of formatting was already
>> required (but silently ignored) for this option to be really taken into
>> account. Only the kernel code was available to understand how to
>> effectively create such hash.
> 
> Great, thanks.
> 
> 
>>>
>>> /Jarkko
>>>
> 
> 
> /Jarkko
>
Jarkko Sakkinen Jan. 21, 2021, 3:21 p.m. UTC | #5 
On Thu, Jan 21, 2021 at 10:18:20AM +0100, Mickaël Salaün wrote:
> 
> On 21/01/2021 00:53, Jarkko Sakkinen wrote:
> > On Wed, Jan 20, 2021 at 12:57:55PM +0100, Mickaël Salaün wrote:
> >>
> >> On 20/01/2021 06:19, Jarkko Sakkinen wrote:
> >>> On Thu, Jan 14, 2021 at 04:19:07PM +0100, Mickaël Salaün wrote:
> >>>> From: Mickaël Salaün <mic@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@redhat.com>
> >>>> Cc: David Woodhouse <dwmw2@infradead.org>
> >>>> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
> >>>> Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
> >>>
> >>> I get this with a self-signed cert:
> >>>
> >>> certs/Makefile:18: *** target pattern contains no '%'.  Stop.
> >>>
> >>> CONFIG_SYSTEM_BLACKLIST_HASH_LIST="tbs:8eed1340eef37c1dc84d996406ad05c7dbb3eade19132d688408ca2f63904869"
> >>
> >> As said in the Kconfig documentation for
> >> CONFIG_SYSTEM_BLACKLIST_HASH_LIST, you need to provide a file with the
> >> list, not to set the string directly in the configuration variable. This
> >> patch series didn't change this behavior. The same kind of macros are
> >> used for CONFIG_MODULE_SIG_KEY.
> > 
> > OK, the documentation just states that:
> > 
> > "Hashes to be preloaded into the system blacklist keyring"
> > 
> > No mention about a file. I'd add a patch to update this documentation.
> 
> I was referring to the full description:
> 
> config SYSTEM_BLACKLIST_HASH_LIST
> 	string "Hashes to be preloaded into the system blacklist keyring"
> 	depends on SYSTEM_BLACKLIST_KEYRING
> 	help
> 	  If set, this option should be the filename of a list of hashes in the
> 	  form "<hash>", "<hash>", ... .  This will be included into a C
> 	  wrapper to incorporate the list into the kernel.  Each <hash> should
> 	  be a string of hex digits.
> 
> …but the short description doesn't mention filename.

Aah.

Anyway, I'll test the next version. Now all should be clear how
to approach that. Thanks.

/Jarkko
diff mbox series

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index cc1e6a5ee6e6..bda31ccbfad0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4120,6 +4120,7 @@  L:	keyrings@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..eb45407ff282 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 $(srctree)/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..107c1d3204d4
--- /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@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-f]+)$", 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;
+	}
+}