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

Kees Cook
2022-05-04T01:49:13Z

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@linux.ibm.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-integrity@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Kees Cook <keescook@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