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sbin/decryptcore/decryptcore.c

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/*-
* Copyright (c) 2015 Konrad Witaszczyk <def@FreeBSD.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
oshogboUnsubmitted
Done
Inline Actions

Missing cdefs and __FBSDID.

oshogbo: Missing cdefs and __FBSDID.
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <sys/capsicum.h>
#include <sys/endian.h>
#include <sys/kerneldump.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/wait.h>
#include <ctype.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <openssl/evp.h>
#include <openssl/pem.h>
#include <openssl/rsa.h>
#include <openssl/engine.h>
#include "pjdlog.h"
cemUnsubmitted
Done
Inline Actions

I believe openssl headers and pjdlog should be in block(s) following standard C headers.

cem: I believe openssl headers and pjdlog should be in block(s) following standard C headers.
#define DECRYPTCORE_CRASHDIR "/var/crash"
static void
usage(void)
{
pjdlog_exitx(1,
"usage: decryptcore [-Lv] -p privatekey -k key -e encryptedcore -c core\n"
" decryptcore [-Lv] [-d crashdir] -p privatekey -n dumpnr");
}
static int
wait_for_process(pid_t pid)
{
int status;
if (waitpid(pid, &status, WUNTRACED | WEXITED) == -1) {
pjdlog_errno(LOG_ERR, "Unable to wait for a child process");
return (1);
}
if (WIFEXITED(status))
return (WEXITSTATUS(status));
return (1);
}
static struct kerneldumpkey *
read_key(int kfd)
{
struct kerneldumpkey *kdk;
ssize_t size;
size_t kdksize;
PJDLOG_ASSERT(kfd >= 0);
kdksize = sizeof(*kdk);
kdk = calloc(1, kdksize);
if (kdk == NULL) {
pjdlog_errno(LOG_ERR, "Unable to allocate kernel dump key");
goto failed;
}
size = read(kfd, kdk, kdksize);
if (size == (ssize_t)kdksize) {
kdk->kdk_encryptedkeysize = dtoh32(kdk->kdk_encryptedkeysize);
kdksize += (size_t)kdk->kdk_encryptedkeysize;
kdk = realloc(kdk, kdksize);
if (kdk == NULL) {
pjdlog_errno(LOG_ERR, "Unable to reallocate kernel dump key");
goto failed;
}
size += read(kfd, &kdk->kdk_encryptedkey,
kdk->kdk_encryptedkeysize);
}
if (size != (ssize_t)kdksize) {
pjdlog_errno(LOG_ERR, "Unable to read key");
goto failed;
}
return (kdk);
failed:
free(kdk);
return (NULL);
}
static bool
decrypt(const char *privkeyfile, const char *keyfile, const char *input,
const char *output)
{
uint8_t buf[KERNELDUMP_BUFFER_SIZE], key[KERNELDUMP_KEY_MAX_SIZE];
EVP_CIPHER_CTX ctx;
const EVP_CIPHER *cipher;
FILE *fp;
struct kerneldumpkey *kdk;
RSA *privkey;
int ifd, kfd, ofd, olen, privkeysize;
ssize_t bytes;
pid_t pid;
PJDLOG_ASSERT(privkeyfile != NULL);
PJDLOG_ASSERT(keyfile != NULL);
PJDLOG_ASSERT(input != NULL);
PJDLOG_ASSERT(output != NULL);
privkey = NULL;
/*
* Decrypt a core dump in a child process so we can unlink a partially
* decrypted core if the child process fails.
*/
pid = fork();
if (pid == -1) {
pjdlog_errno(LOG_ERR, "Unable to create child process");
return (false);
}
if (pid > 0)
return (wait_for_process(pid) == 0);
kfd = open(keyfile, O_RDONLY);
if (kfd == -1) {
pjdlog_errno(LOG_ERR, "Unable to open %s", keyfile);
goto failed;
}
ifd = open(input, O_RDONLY);
if (ifd == -1) {
pjdlog_errno(LOG_ERR, "Unable to open %s", input);
goto failed;
}
ofd = open(output, O_WRONLY | O_CREAT | O_TRUNC, 0600);
if (ofd == -1) {
pjdlog_errno(LOG_ERR, "Unable to open %s", output);
goto failed;
}
fp = fopen(privkeyfile, "r");
if (fp == NULL) {
pjdlog_errno(LOG_ERR, "Unable to open %s", privkeyfile);
goto failed;
}
if (cap_enter() < 0 && errno != ENOSYS) {
pjdlog_errno(LOG_ERR, "Unable to enter capability mode");
goto failed;
}
privkey = RSA_new();
if (privkey == NULL) {
pjdlog_error("Unable to allocate an RSA structure: %s",
ERR_error_string(ERR_get_error(), NULL));
goto failed;
}
EVP_CIPHER_CTX_init(&ctx);
kdk = read_key(kfd);
close(kfd);
if (kdk == NULL)
goto failed;
delphijUnsubmitted
Done
Inline Actions

Should we disable coredump at this point if not debugging? Otherwise it may defeat the purpose if the process crashes.

delphij: Should we disable coredump at this point if not debugging? Otherwise it may defeat the purpose…
oshogboUnsubmitted
Done
Inline Actions

Every where where you using cap_enter it should be checked like that:
cap_enter() < 0 && errno != ENOSYS
As far as I know dumps can work without CAPSICUM.

oshogbo: Every where where you using cap_enter it should be checked like that: cap_enter() < 0 && errno !
defAuthorUnsubmitted
Done
Inline Actions

It's assumed that disabling Capsicum doesn't disable a functionality which uses Capsicum.

def: It's assumed that disabling Capsicum doesn't disable a functionality which uses Capsicum.
privkey = PEM_read_RSAPrivateKey(fp, &privkey, NULL, NULL);
fclose(fp);
if (privkey == NULL) {
pjdlog_error("Unable to read data from %s.", privkeyfile);
delphijUnsubmitted
Done
Inline Actions

Is there some reason that this section (193-199) is done after entering capability mode? (Or other words, can they be moved to before opening the files?)

delphij: Is there some reason that this section (193-199) is done after entering capability mode? (Or…
pjdUnsubmitted
Done
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Why do you want to increase TCB? Even if the code doesn't introduce any risk now, it may be modified in the future. I'd need to hear a convincing argument to agree on this one:)

pjd: Why do you want to increase TCB? Even if the code doesn't introduce any risk now, it may be…
defAuthorUnsubmitted
Done
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As Paweł said we don't want to perform any unnecessary operation before entering capability mode.

def: As Paweł said we don't want to perform any unnecessary operation before entering capability…
goto failed;
}
privkeysize = RSA_size(privkey);
if (privkeysize != (int)kdk->kdk_encryptedkeysize) {
pjdlog_error("RSA modulus size mismatch: equals %db and should be %ub.",
8 * privkeysize, 8 * kdk->kdk_encryptedkeysize);
goto failed;
}
switch (kdk->kdk_encryption) {
case KERNELDUMP_ENC_AES_256_CBC:
cipher = EVP_aes_256_cbc();
break;
default:
pjdlog_error("Invalid encryption algorithm.");
goto failed;
}
if (RSA_private_decrypt(kdk->kdk_encryptedkeysize,
kdk->kdk_encryptedkey, key, privkey,
RSA_PKCS1_PADDING) != sizeof(key)) {
pjdlog_error("Unable to decrypt key: %s",
ERR_error_string(ERR_get_error(), NULL));
goto failed;
}
RSA_free(privkey);
privkey = NULL;
EVP_DecryptInit_ex(&ctx, cipher, NULL, key, kdk->kdk_iv);
EVP_CIPHER_CTX_set_padding(&ctx, 0);
explicit_bzero(key, sizeof(key));
do {
bytes = read(ifd, buf, sizeof(buf));
if (bytes < 0) {
pjdlog_errno(LOG_ERR, "Unable to read data from %s",
input);
goto failed;
} else if (bytes == 0) {
break;
}
if (bytes > 0) {
if (EVP_DecryptUpdate(&ctx, buf, &olen, buf,
bytes) == 0) {
pjdlog_error("Unable to decrypt core.");
goto failed;
delphijUnsubmitted
Done
Inline Actions

Perhaps explicit_bzero(3)?

delphij: Perhaps explicit_bzero(3)?
}
} else {
if (EVP_DecryptFinal_ex(&ctx, buf, &olen) == 0) {
pjdlog_error("Unable to decrypt core.");
goto failed;
}
}
if (olen == 0)
continue;
if (write(ofd, buf, olen) != olen) {
pjdlog_errno(LOG_ERR, "Unable to write data to %s",
output);
goto failed;
}
} while (bytes > 0);
explicit_bzero(buf, sizeof(buf));
EVP_CIPHER_CTX_cleanup(&ctx);
exit(0);
failed:
explicit_bzero(key, sizeof(key));
explicit_bzero(buf, sizeof(buf));
RSA_free(privkey);
EVP_CIPHER_CTX_cleanup(&ctx);
exit(1);
}
int
main(int argc, char **argv)
{
char core[PATH_MAX], encryptedcore[PATH_MAX], keyfile[PATH_MAX];
struct stat sb;
const char *crashdir, *dumpnr, *privatekey;
int ch, debug;
size_t ii;
bool usesyslog;
pjdlog_init(PJDLOG_MODE_STD);
pjdlog_prefix_set("(decryptcore) ");
debug = 0;
*core = '\0';
crashdir = NULL;
dumpnr = NULL;
*encryptedcore = '\0';
*keyfile = '\0';
privatekey = NULL;
usesyslog = false;
while ((ch = getopt(argc, argv, "Lc:d:e:k:n:p:v")) != -1) {
switch (ch) {
case 'L':
usesyslog = true;
break;
case 'c':
strncpy(core, optarg, sizeof(core));
break;
case 'd':
crashdir = optarg;
break;
case 'e':
strncpy(encryptedcore, optarg, sizeof(encryptedcore));
break;
case 'k':
strncpy(keyfile, optarg, sizeof(keyfile));
break;
case 'n':
dumpnr = optarg;
break;
case 'p':
privatekey = optarg;
break;
case 'v':
debug++;
delphijUnsubmitted
Done
Inline Actions

This construction is Okay, but if I was you, I would probably go with standard getopt_long which would avoid the hardcoding of parameters and allow more flexible command line options ordering. Just a suggestion.

delphij: This construction is Okay, but if I was you, I would probably go with standard getopt_long…
pjdUnsubmitted
Done
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I'm fine with this suggestion, but I'd stick to regular getopt(3), which should be more than enough here.

pjd: I'm fine with this suggestion, but I'd stick to regular getopt(3), which should be more than…
break;
default:
usage();
}
}
argc -= optind;
argv += optind;
if (argc != 0)
usage();
/* Verify mutually exclusive options. */
if ((crashdir != NULL || dumpnr != NULL) &&
(*keyfile != '\0' || *encryptedcore != '\0' || *core != '\0')) {
usage();
}
/*
* Set key, encryptedcore and core file names using crashdir and dumpnr.
oshogboUnsubmitted
Done
Inline Actions

Why just don't use
output = argv[3] ?
and so any.
Code would be a little bit smaller.

oshogbo: Why just don't use output = argv[3] ? and so any. Code would be a little bit smaller.
*/
if (dumpnr != NULL) {
for (ii = 0; ii < strnlen(dumpnr, PATH_MAX); ii++) {
if (isdigit((int)dumpnr[ii]) == 0)
usage();
}
if (crashdir == NULL)
crashdir = DECRYPTCORE_CRASHDIR;
PJDLOG_VERIFY(snprintf(keyfile, sizeof(keyfile),
"%s/key.%s", crashdir, dumpnr) > 0);
PJDLOG_VERIFY(snprintf(core, sizeof(core),
"%s/vmcore.%s", crashdir, dumpnr) > 0);
PJDLOG_VERIFY(snprintf(encryptedcore, sizeof(encryptedcore),
"%s/vmcore_encrypted.%s", crashdir, dumpnr) > 0);
}
if (privatekey == NULL || *keyfile == '\0' || *encryptedcore == '\0' ||
*core == '\0') {
usage();
}
if (usesyslog)
pjdlog_mode_set(PJDLOG_MODE_SYSLOG);
pjdlog_debug_set(debug);
if (!decrypt(privatekey, keyfile, encryptedcore, core)) {
if (stat(core, &sb) == 0 && unlink(core) != 0)
pjdlog_exit(1, "Unable to remove core");
exit(1);
}
pjdlog_fini();
exit(0);
}