linux/security/integrity/digsig_asymmetric.c
Mikhail Kurinnoi 6eb864c1d9 integrity: prevent deadlock during digsig verification.
This patch aimed to prevent deadlock during digsig verification.The point
of issue - user space utility modprobe and/or it's dependencies (ld-*.so,
libz.so.*, libc-*.so and /lib/modules/ files) that could be used for
kernel modules load during digsig verification and could be signed by
digsig in the same time.

First at all, look at crypto_alloc_tfm() work algorithm:
crypto_alloc_tfm() will first attempt to locate an already loaded
algorithm. If that fails and the kernel supports dynamically loadable
modules, it will then attempt to load a module of the same name or alias.
If that fails it will send a query to any loaded crypto manager to
construct an algorithm on the fly.

We have situation, when public_key_verify_signature() in case of RSA
algorithm use alg_name to store internal information in order to construct
an algorithm on the fly, but crypto_larval_lookup() will try to use
alg_name in order to load kernel module with same name.

1) we can't do anything with crypto module work, since it designed to work
exactly in this way;
2) we can't globally filter module requests for modprobe, since it
designed to work with any requests.

In this patch, I propose add an exception for "crypto-pkcs1pad(rsa,*)"
module requests only in case of enabled integrity asymmetric keys support.
Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel modules for
sure, we are safe to fail such module request from crypto_larval_lookup().
In this way we prevent modprobe execution during digsig verification and
avoid possible deadlock if modprobe and/or it's dependencies also signed
with digsig.

Requested "crypto-pkcs1pad(rsa,*)" kernel module name formed by:
1) "pkcs1pad(rsa,%s)" in public_key_verify_signature();
2) "crypto-%s" / "crypto-%s-all" in crypto_larval_lookup().
"crypto-pkcs1pad(rsa," part of request is a constant and unique and could
be used as filter.

Signed-off-by: Mikhail Kurinnoi <viewizard@viewizard.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

 include/linux/integrity.h              | 13 +++++++++++++
 security/integrity/digsig_asymmetric.c | 23 +++++++++++++++++++++++
 security/security.c                    |  7 ++++++-
 3 files changed, 42 insertions(+), 1 deletion(-)
2018-07-18 07:27:22 -04:00

141 lines
3.4 KiB
C

/*
* Copyright (C) 2013 Intel Corporation
*
* Author:
* Dmitry Kasatkin <dmitry.kasatkin@intel.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 2 of the License.
*
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/err.h>
#include <linux/ratelimit.h>
#include <linux/key-type.h>
#include <crypto/public_key.h>
#include <crypto/hash_info.h>
#include <keys/asymmetric-type.h>
#include <keys/system_keyring.h>
#include "integrity.h"
/*
* Request an asymmetric key.
*/
static struct key *request_asymmetric_key(struct key *keyring, uint32_t keyid)
{
struct key *key;
char name[12];
sprintf(name, "id:%08x", keyid);
pr_debug("key search: \"%s\"\n", name);
key = get_ima_blacklist_keyring();
if (key) {
key_ref_t kref;
kref = keyring_search(make_key_ref(key, 1),
&key_type_asymmetric, name);
if (!IS_ERR(kref)) {
pr_err("Key '%s' is in ima_blacklist_keyring\n", name);
return ERR_PTR(-EKEYREJECTED);
}
}
if (keyring) {
/* search in specific keyring */
key_ref_t kref;
kref = keyring_search(make_key_ref(keyring, 1),
&key_type_asymmetric, name);
if (IS_ERR(kref))
key = ERR_CAST(kref);
else
key = key_ref_to_ptr(kref);
} else {
key = request_key(&key_type_asymmetric, name, NULL);
}
if (IS_ERR(key)) {
pr_err_ratelimited("Request for unknown key '%s' err %ld\n",
name, PTR_ERR(key));
switch (PTR_ERR(key)) {
/* Hide some search errors */
case -EACCES:
case -ENOTDIR:
case -EAGAIN:
return ERR_PTR(-ENOKEY);
default:
return key;
}
}
pr_debug("%s() = 0 [%x]\n", __func__, key_serial(key));
return key;
}
int asymmetric_verify(struct key *keyring, const char *sig,
int siglen, const char *data, int datalen)
{
struct public_key_signature pks;
struct signature_v2_hdr *hdr = (struct signature_v2_hdr *)sig;
struct key *key;
int ret = -ENOMEM;
if (siglen <= sizeof(*hdr))
return -EBADMSG;
siglen -= sizeof(*hdr);
if (siglen != be16_to_cpu(hdr->sig_size))
return -EBADMSG;
if (hdr->hash_algo >= HASH_ALGO__LAST)
return -ENOPKG;
key = request_asymmetric_key(keyring, be32_to_cpu(hdr->keyid));
if (IS_ERR(key))
return PTR_ERR(key);
memset(&pks, 0, sizeof(pks));
pks.pkey_algo = "rsa";
pks.hash_algo = hash_algo_name[hdr->hash_algo];
pks.digest = (u8 *)data;
pks.digest_size = datalen;
pks.s = hdr->sig;
pks.s_size = siglen;
ret = verify_signature(key, &pks);
key_put(key);
pr_debug("%s() = %d\n", __func__, ret);
return ret;
}
/**
* integrity_kernel_module_request - prevent crypto-pkcs1pad(rsa,*) requests
* @kmod_name: kernel module name
*
* We have situation, when public_key_verify_signature() in case of RSA
* algorithm use alg_name to store internal information in order to
* construct an algorithm on the fly, but crypto_larval_lookup() will try
* to use alg_name in order to load kernel module with same name.
* Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel modules,
* we are safe to fail such module request from crypto_larval_lookup().
*
* In this way we prevent modprobe execution during digsig verification
* and avoid possible deadlock if modprobe and/or it's dependencies
* also signed with digsig.
*/
int integrity_kernel_module_request(char *kmod_name)
{
if (strncmp(kmod_name, "crypto-pkcs1pad(rsa,", 20) == 0)
return -EINVAL;
return 0;
}