linux-kernel - [PATCH 2/3] module: strip the signature marker in the verification function.

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Message-Id: <8c183211d3980554b046a1cc215f3b0f1ca17072.1635948742.git.msuchanek@suse.de>
Date:   Wed,  3 Nov 2021 15:27:07 +0100
From:   Michal Suchanek <msuchanek@...e.de>
To:     keyrings@...r.kernel.org
Cc:     Michal Suchanek <msuchanek@...e.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Jessica Yu <jeyu@...nel.org>, Rob Herring <robh@...nel.org>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Frank van der Linden <fllinden@...zon.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: [PATCH 2/3] module: strip the signature marker in the verification function.

It is stripped by each caller separately.

Signed-off-by: Michal Suchanek <msuchanek@...e.de>
---
 arch/s390/kernel/machine_kexec_file.c |  9 ---------
 kernel/module.c                       |  7 +------
 kernel/module_signing.c               | 12 ++++++++++--
 3 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c
index 634e641cd8aa..82260bb61060 100644
--- a/arch/s390/kernel/machine_kexec_file.c
+++ b/arch/s390/kernel/machine_kexec_file.c
@@ -26,20 +26,11 @@ const struct kexec_file_ops * const kexec_file_loaders[] = {
 int s390_verify_sig(const char *kernel, unsigned long length)
 {
 	size_t kernel_len = length;
-	const unsigned long marker_len = sizeof(MODULE_SIG_STRING) - 1;
 
 	/* Skip signature verification when not secure IPLed. */
 	if (!ipl_secure_flag)
 		return 0;
 
-	if (marker_len > kernel_len)
-		return -EKEYREJECTED;
-
-	if (memcmp(kernel + kernel_len - marker_len, MODULE_SIG_STRING,
-		   marker_len))
-		return -EKEYREJECTED;
-	kernel_len -= marker_len;
-
 	return verify_appended_signature(kernel, &kernel_len, VERIFY_USE_PLATFORM_KEYRING,
 					"kexec_file");
 }
diff --git a/kernel/module.c b/kernel/module.c
index 137b3661be75..1c421b0442e3 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2882,7 +2882,6 @@ static inline void kmemleak_load_module(const struct module *mod,
 static int module_sig_check(struct load_info *info, int flags)
 {
 	int err = -ENODATA;
-	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
 	const char *reason;
 	const void *mod = info->hdr;
 
@@ -2890,11 +2889,7 @@ static int module_sig_check(struct load_info *info, int flags)
 	 * Require flags == 0, as a module with version information
 	 * removed is no longer the module that was signed
 	 */
-	if (flags == 0 &&
-	    info->len > markerlen &&
-	    memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
-		/* We truncate the module to discard the signature */
-		info->len -= markerlen;
+	if (flags == 0) {
 		err = verify_appended_signature(mod, &info->len,
 						VERIFY_USE_SECONDARY_KEYRING, "module");
 		if (!err) {
diff --git a/kernel/module_signing.c b/kernel/module_signing.c
index f492e410564d..4c28cb55275f 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -15,8 +15,7 @@
 #include "module-internal.h"
 
 /**
- * verify_appended_signature - Verify the signature on a module with the
- * signature marker stripped.
+ * verify_appended_signature - Verify the signature on a module
  * @data: The data to be verified
  * @len: Size of @data.
  * @trusted_keys: Keyring to use for verification
@@ -25,12 +24,21 @@
 int verify_appended_signature(const void *data, size_t *len,
 			      struct key *trusted_keys, const char *what)
 {
+	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
 	struct module_signature ms;
 	size_t sig_len, modlen = *len;
 	int ret;
 
 	pr_devel("==>%s(,%zu)\n", __func__, modlen);
 
+	if (markerlen > modlen)
+		return -ENODATA;
+
+	if (memcmp(data + modlen - markerlen, MODULE_SIG_STRING,
+		   markerlen))
+		return -ENODATA;
+	modlen -= markerlen;
+
 	if (modlen <= sizeof(ms))
 		return -EBADMSG;
 
-- 
2.31.1