[PATCH v4 08/17] module: Deduplicate signature extraction

["Thomas Weißschuh" <linux@weissschuh.net>]

The logic to extract the signature bits from a module file are
duplicated between the module core and IMA modsig appraisal.

Unify the implementation.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 include/linux/module_signature.h    |  4 +--
 kernel/module/signing.c             | 52 +++++++------------------------------
 kernel/module_signature.c           | 41 +++++++++++++++++++++++++++--
 security/integrity/ima/ima_modsig.c | 24 ++++-------------
 4 files changed, 56 insertions(+), 65 deletions(-)

diff --git a/include/linux/module_signature.h b/include/linux/module_signature.h
index 7eb4b00381ac..186a55effa30 100644
--- a/include/linux/module_signature.h
+++ b/include/linux/module_signature.h
@@ -40,7 +40,7 @@ struct module_signature {
 	__be32	sig_len;	/* Length of signature data */
 };
 
-int mod_check_sig(const struct module_signature *ms, size_t file_len,
-		  const char *name);
+int mod_split_sig(const void *buf, size_t *buf_len, bool mangled,
+		  size_t *sig_len, const u8 **sig, const char *name);
 
 #endif /* _LINUX_MODULE_SIGNATURE_H */
diff --git a/kernel/module/signing.c b/kernel/module/signing.c
index fe3f51ac6199..6d64c0d18d0a 100644
--- a/kernel/module/signing.c
+++ b/kernel/module/signing.c
@@ -37,54 +37,22 @@ void set_module_sig_enforced(void)
 	sig_enforce = true;
 }
 
-/*
- * Verify the signature on a module.
- */
-static int mod_verify_sig(const void *mod, struct load_info *info)
-{
-	struct module_signature ms;
-	size_t sig_len, modlen = info->len;
-	int ret;
-
-	pr_devel("==>%s(,%zu)\n", __func__, modlen);
-
-	if (modlen <= sizeof(ms))
-		return -EBADMSG;
-
-	memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
-
-	ret = mod_check_sig(&ms, modlen, "module");
-	if (ret)
-		return ret;
-
-	sig_len = be32_to_cpu(ms.sig_len);
-	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);
-}
-
 int module_sig_check(struct load_info *info, int flags)
 {
-	int err = -ENODATA;
-	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
+	int err;
 	const char *reason;
 	const void *mod = info->hdr;
+	size_t sig_len;
+	const u8 *sig;
 	bool mangled_module = flags & (MODULE_INIT_IGNORE_MODVERSIONS |
 				       MODULE_INIT_IGNORE_VERMAGIC);
-	/*
-	 * Do not allow mangled modules as a module with version information
-	 * removed is no longer the module that was signed.
-	 */
-	if (!mangled_module &&
-	    info->len > markerlen &&
-	    memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
-		/* We truncate the module to discard the signature */
-		info->len -= markerlen;
-		err = mod_verify_sig(mod, info);
+
+	err = mod_split_sig(info->hdr, &info->len, mangled_module, &sig_len, &sig, "module");
+	if (!err) {
+		err = verify_pkcs7_signature(mod, info->len, sig, sig_len,
+					     VERIFY_USE_SECONDARY_KEYRING,
+					     VERIFYING_MODULE_SIGNATURE,
+					     NULL, NULL);
 		if (!err) {
 			info->sig_ok = true;
 			return 0;
diff --git a/kernel/module_signature.c b/kernel/module_signature.c
index 00132d12487c..b2384a73524c 100644
--- a/kernel/module_signature.c
+++ b/kernel/module_signature.c
@@ -8,6 +8,7 @@
 
 #include <linux/errno.h>
 #include <linux/printk.h>
+#include <linux/string.h>
 #include <linux/module_signature.h>
 #include <asm/byteorder.h>
 
@@ -18,8 +19,8 @@
  * @file_len:	Size of the file to which @ms is appended.
  * @name:	What is being checked. Used for error messages.
  */
-int mod_check_sig(const struct module_signature *ms, size_t file_len,
-		  const char *name)
+static int mod_check_sig(const struct module_signature *ms, size_t file_len,
+			 const char *name)
 {
 	if (be32_to_cpu(ms->sig_len) >= file_len - sizeof(*ms))
 		return -EBADMSG;
@@ -44,3 +45,39 @@ int mod_check_sig(const struct module_signature *ms, size_t file_len,
 
 	return 0;
 }
+
+int mod_split_sig(const void *buf, size_t *buf_len, bool mangled,
+		  size_t *sig_len, const u8 **sig, const char *name)
+{
+	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
+	struct module_signature ms;
+	size_t modlen = *buf_len;
+	int ret;
+
+	/*
+	 * Do not allow mangled modules as a module with version information
+	 * removed is no longer the module that was signed.
+	 */
+	if (!mangled &&
+	    *buf_len > markerlen &&
+	    memcmp(buf + modlen - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
+		/* We truncate the module to discard the signature */
+		modlen -= markerlen;
+	}
+
+	if (modlen <= sizeof(ms))
+		return -EBADMSG;
+
+	memcpy(&ms, buf + (modlen - sizeof(ms)), sizeof(ms));
+
+	ret = mod_check_sig(&ms, modlen, name);
+	if (ret)
+		return ret;
+
+	*sig_len = be32_to_cpu(ms.sig_len);
+	modlen -= *sig_len + sizeof(ms);
+	*buf_len = modlen;
+	*sig = buf + modlen;
+
+	return 0;
+}
diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index 3265d744d5ce..a57342d39b07 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -40,44 +40,30 @@ struct modsig {
 int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
 		    struct modsig **modsig)
 {
-	const size_t marker_len = strlen(MODULE_SIG_STRING);
-	const struct module_signature *sig;
+	size_t buf_len_sz = buf_len;
 	struct modsig *hdr;
 	size_t sig_len;
-	const void *p;
+	const u8 *sig;
 	int rc;
 
-	if (buf_len <= marker_len + sizeof(*sig))
-		return -ENOENT;
-
-	p = buf + buf_len - marker_len;
-	if (memcmp(p, MODULE_SIG_STRING, marker_len))
-		return -ENOENT;
-
-	buf_len -= marker_len;
-	sig = (const struct module_signature *)(p - sizeof(*sig));
-
-	rc = mod_check_sig(sig, buf_len, func_tokens[func]);
+	rc = mod_split_sig(buf, &buf_len_sz, true, &sig_len, &sig, func_tokens[func]);
 	if (rc)
 		return rc;
 
-	sig_len = be32_to_cpu(sig->sig_len);
-	buf_len -= sig_len + sizeof(*sig);
-
 	/* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
 	hdr = kzalloc(struct_size(hdr, raw_pkcs7, sig_len), GFP_KERNEL);
 	if (!hdr)
 		return -ENOMEM;
 
 	hdr->raw_pkcs7_len = sig_len;
-	hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
+	hdr->pkcs7_msg = pkcs7_parse_message(sig, sig_len);
 	if (IS_ERR(hdr->pkcs7_msg)) {
 		rc = PTR_ERR(hdr->pkcs7_msg);
 		kfree(hdr);
 		return rc;
 	}
 
-	memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
+	memcpy(hdr->raw_pkcs7, sig, sig_len);
 
 	/* We don't know the hash algorithm yet. */
 	hdr->hash_algo = HASH_ALGO__LAST;

-- 
2.52.0