[PATCH 26/32] ima: Use mem_to_flex_dup() with struct modsig

[Kees Cook]

As part of the work to perform bounds checking on all memcpy() uses,
replace the open-coded a deserialization of bytes out of memory into a
trailing flexible array by using a flex_array.h helper to perform the
allocation, bounds checking, and copying.

Cc: Mimi Zohar <zohar at linux.ibm.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin at gmail.com>
Cc: James Morris <jmorris at namei.org>
Cc: "Serge E. Hallyn" <serge at hallyn.com>
Cc: linux-integrity at vger.kernel.org
Cc: linux-security-module at vger.kernel.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 security/integrity/ima/ima_modsig.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index fb25723c65bc..200c080d36de 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -28,8 +28,8 @@ struct modsig {
 	 * This is what will go to the measurement list if the template requires
 	 * storing the signature.
 	 */
-	int raw_pkcs7_len;
-	u8 raw_pkcs7[];
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(int, raw_pkcs7_len);
+	DECLARE_FLEX_ARRAY_ELEMENTS(u8, raw_pkcs7);
 };
 
 /*
@@ -42,7 +42,7 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
 {
 	const size_t marker_len = strlen(MODULE_SIG_STRING);
 	const struct module_signature *sig;
-	struct modsig *hdr;
+	struct modsig *hdr = NULL;
 	size_t sig_len;
 	const void *p;
 	int rc;
@@ -65,8 +65,7 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
 	buf_len -= sig_len + sizeof(*sig);
 
 	/* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
-	hdr = kzalloc(sizeof(*hdr) + sig_len, GFP_KERNEL);
-	if (!hdr)
+	if (mem_to_flex_dup(&hdr, buf + buf_len, sig_len, GFP_KERNEL))
 		return -ENOMEM;
 
 	hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
@@ -76,9 +75,6 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
 		return rc;
 	}
 
-	memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
-	hdr->raw_pkcs7_len = sig_len;
-
 	/* We don't know the hash algorithm yet. */
 	hdr->hash_algo = HASH_ALGO__LAST;
 
-- 
2.32.0