WIP: Adds MbedTLS support to Cytoplasm #54

Draft
lda wants to merge 9 commits from lda/Cytoplasm:add-mbed into master
8 changed files with 451 additions and 3 deletions

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@ -5,6 +5,20 @@ Cytoplasm. It is intended to be updated with every commit that makes a user-faci
change worth reporting in the change log. As such, it changes frequently between
releases. Final change log entries are published as [Releases](releases).
## v0.5.0
**TO BE WRITTEN**
### Breaking Changes
- `ShaToHex` now requires what hash was used.
### New Features
- LMDB support is available with the `--with-lmdb` flag.
- MbedTLS summort is available with the `--with-mbed` flag. Please note that Cytoplasm
programs using it must be used with the `CYTO_TLS_CA` environment defined to map to a
valid CA file, and that the `CYTO_TLS_SEED` flag can be set to use a seedfile, increasing
entropy on systems where it is unavailable.
## v0.4.1
Cytoplasm is now a C99 library! Upgrading from C89 to C99 makes Cytoplasm more portable

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@ -21,6 +21,7 @@ Cytoplasm aims to have zero software dependencies beyond what is mandated by POS
- OpenSSL
- LibreSSL
- MbedTLS (requires the `CYTO_TLS_CA` environment variables for programs built with it)
If TLS support is not enabled, all APIs that use it should fall back to non-TLS behavior in a sensible manner. For example, if TLS support is not enabled, then the HTTP client API will simply return an error if a TLS connection is requested.
@ -50,7 +51,7 @@ You can also run `make install` as `root` to install Cytoplasm to the system. Th
The `configure` script has a number of optional flags, which are as follows:
- `--with-(openssl|libressl)`: Select the TLS implementation to use. OpenSSL is selected by default.
- `--with-(openssl|libressl|mbed)`: Select the TLS implementation to use. OpenSSL is selected by default.
- `--disable-tls`: Disable TLS altogether.
- `--prefix=<path>`: Set the install prefix to set by default in the `Makefile`. This defaults to `/usr/local`, which should be appropriate for most Unix-like systems.
- `--(enable|disable)-debug`: Control whether or not to enable debug mode. This sets the optimization level to 0 and builds with debug symbols. Useful for running with a debugger.

4
configure vendored
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@ -76,6 +76,10 @@ for arg in $SCRIPT_ARGS; do
TLS_IMPL="TLS_LIBRESSL"
TLS_LIBS="-ltls -lcrypto -lssl"
;;
--with-mbed)
TLS_IMPL="TLS_MBEDTLS"
TLS_LIBS="-lmbedtls -lmbedx509 -lmbedcrypto"
;;
--disable-tls)
TLS_IMPL=""
TLS_LIBS=""

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@ -50,6 +50,7 @@
#define TLS_LIBRESSL 2
#define TLS_OPENSSL 3
#define TLS_MBEDTLS 4
/**
* Create a new TLS client stream using the given file descriptor and

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@ -29,6 +29,7 @@
#include <limits.h>
/* TODO: Verify LibreSSL support later */
#include <Tls.h>
#if defined(TLS_IMPL) && (TLS_IMPL == TLS_OPENSSL)
#include <openssl/sha.h>

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@ -31,6 +31,7 @@
/* TODO: Verify LibreSSL support later */
#include <Tls.h>
#if defined(TLS_IMPL) && (TLS_IMPL == TLS_OPENSSL)
#include <openssl/sha.h>

426
src/Tls/TlsMbedTLS.c Normal file
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@ -0,0 +1,426 @@
/*
* Copyright (C) 2022-2024 Jordan Bancino <@jordan:bancino.net> with
* other valuable contributors. See CONTRIBUTORS.txt for the full list.
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation files
* (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge,
* publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include <Tls.h>
#if TLS_IMPL == TLS_MBEDTLS
#include "mbedtls/net_sockets.h"
#include "mbedtls/ssl.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/debug.h"
#include "mbedtls/error.h"
#include <Memory.h>
#include <Log.h>
#include <Str.h>
#include <string.h>
#include <stdlib.h>
/*
* #include statements and any implementation structures
* needed should go here.
*/
typedef struct MbedCookie {
int fd;
bool serverside;
mbedtls_net_context serverFD;
mbedtls_entropy_context entropy;
mbedtls_ctr_drbg_context ctrDrbg;
mbedtls_ssl_context ssl;
mbedtls_ssl_config conf;
mbedtls_x509_crt cert;
mbedtls_pk_context serverkey;
} MbedCookie;
static bool
AddPEM(mbedtls_x509_crt *certs, char *path)
{
size_t len;
if (!certs || !path)
{
return false;
}
len = strlen(path);
if (len >= 4 && StrEquals(&path[len - 1 - 4], ".pem"))
{
/* Parse it as a file */
if (mbedtls_x509_crt_parse_file(certs, path) == 0)
{
return true;
}
}
/* Parse it as a directory if it is not a .PEM
* Note that this is non-recursive. */
return mbedtls_x509_crt_parse_path(certs, path) == 0;
}
static bool
RegisterPEMs(mbedtls_x509_crt *certs)
{
char *cafile;
int loaded = 0;
if (!certs)
{
return false;
}
/* Step 0: Load from CYTO_TLS_CA if present to overwrite */
cafile = getenv("CYTO_TLS_CA");
if (AddPEM(certs, cafile))
{
loaded++;
}

Forgive me for not understanding MbedTLS that well, but why does this need to be sourced from the environment? Can't we randomly generate a seed? What's the use case for using the same seed more than once?

Forgive me for not understanding MbedTLS that well, but why does this need to be sourced from the environment? Can't we randomly generate a seed? What's the use case for using the same seed more than once?
Outdated
Review

It doesn't have to in most cases(MbedTLS will try to use things like /dev/random if possible) but considering how POSIX doesn't really mandate such sources to exist in the first place (and that I really wouldn't use something like the Rand API for cryptographic tasks), and I think having an optional source of extra randomness, if possible, may be worth it.

What's the use case for using the same seed more than once?
MbdeTLS tends to change the seed anyways with whatever other sources it can grab too.

It *doesn't* have to in most cases(MbedTLS will try to use things like `/dev/random` if possible) but considering how POSIX doesn't really mandate such sources to exist in the first place (and that I really *wouldn't* use something like the `Rand` API for cryptographic tasks), and I think having an optional source of extra randomness, if possible, may be worth it. > What's the use case for using the same seed more than once? MbdeTLS tends to change the seed anyways with whatever other sources it can grab too.

(and that I really wouldn't use something like the Rand API for cryptographic tasks)

I agree, and that's the real problem here. Ideally, we should use the Rand API to generate the MbedTLS seed. The fact that we can't because Rand isn't cryptographically secure is a problem of its own that, in my opinion, should be fixed first before we start relying on environment variables.

I'd like Cytoplasm to very much be link-and-forget. It shouldn't have any special runtime dependencies like this. I don't even know how we'd trust the user to set the seed properly. If the system doesn't have some source of entropy that we can draw from, then I don't know how the user could generate a seed. Because if they can do it on the machine we're running on, then so can we, and so should we. Otherwise, they'd have to generate it on a different machine and then copy it over to the machine executing this Cytoplasm code? That seems pretty impractical, particularly because every time Cytoplasm is started, (or every time this function is called?) the seed needs to be freshly generated.

> (and that I really wouldn't use something like the Rand API for cryptographic tasks) I agree, and that's the real problem here. Ideally, we *should* use the Rand API to generate the MbedTLS seed. The fact that we can't because Rand isn't cryptographically secure is a problem of its own that, in my opinion, should be fixed first before we start relying on environment variables. I'd like Cytoplasm to very much be link-and-forget. It shouldn't have any special runtime dependencies like this. I don't even know how we'd trust the user to set the seed properly. If the system doesn't have some source of entropy that we can draw from, then I don't know how the user *could* generate a seed. Because if they can do it on the machine we're running on, then so can we, and so should we. Otherwise, they'd have to generate it on a different machine and then copy it over to the machine executing this Cytoplasm code? That seems pretty impractical, particularly because every time Cytoplasm is started, (or every time this function is called?) the seed needs to be freshly generated.
/* Step 1: Try /etc/ssl/certs */
if (AddPEM(certs, "/etc/ssl/certs"))
{
loaded++;
}
/* Step 2: Try loading off Mozilla's certificates */
if (AddPEM(certs, "/usr/share/ca-certificates/mozilla"))
{
loaded++;
}
/* Step 3: Try loading from its root directly */
if (AddPEM(certs, "/usr/share/ca-certificates"))
{
loaded++;
}
return loaded != 0;
}
void *

Again, why should this come from the environment? Is there a way we can somehow just use the system's CA file?

Again, why should this come from the environment? Is there a way we can somehow just use the system's CA file?
Outdated
Review

Just made it check for known certificate paths(though I've kept the environment, in case any users may still want to use a custom directory/are really unlucky in their OS setups)

Just made it check for known certificate paths(though I've kept the environment, in case any users may still want to use a custom directory/are really unlucky in their OS setups)

Okay, I think I'm good with what you've done here. I do have a question though: Can you load multiple PEMs? Like, why bother with return true on success, when you could just keep going and load all the CA stores you can find? If the answer is no, you can only load one CA store, then that makes sense. I'm just curious if we could be even more flexible and load multiple.

However, I don't think this behavior should be specific to Mbed. If we're going to use CYTO_TLS_CA to modify Cytoplasm's runtime behavior in loading certificate stores, shouldn't all of the other TLS implementations honor this environment variable too?

For example, say I'm a sysadmin at a large corporation with tons of self-signed certificates for internal services. Instead of installing the certificate authority to the system, I want to just set CYTO_TLS_CA to my CA store. I'm on a Linux system so I can use OpenSSL, but the TLS implementation really shouldn't matter. Though I guess it might determine what format the CA store must be in. But the point is, the behavior should be consistent across all implementations.

Okay, I think I'm good with what you've done here. I do have a question though: Can you load *multiple* PEMs? Like, why bother with `return true` on success, when you could just keep going and load all the CA stores you can find? If the answer is no, you can only load one CA store, then that makes sense. I'm just curious if we could be *even more* flexible and load multiple. **However**, I don't think this behavior should be specific to Mbed. If we're going to use `CYTO_TLS_CA` to modify Cytoplasm's runtime behavior in loading certificate stores, shouldn't all of the *other* TLS implementations honor this environment variable too? For example, say I'm a sysadmin at a large corporation with tons of self-signed certificates for internal services. Instead of installing the certificate authority to the system, I want to just set `CYTO_TLS_CA` to my CA store. I'm on a Linux system so I can use OpenSSL, but the TLS implementation really shouldn't matter. Though I guess it might determine what format the CA store must be in. But the point is, the behavior should be consistent across all implementations.
Outdated
Review

Can you load multiple PEMs?

You actually can(if you look under the MbedTLS hood, loading a directory of PEM files is essentially just loading every PEM directly), so I just added that.

As for the CYTO_TLS_CA, I'm not sure I can exactly replicate that behavior around LibreSSL, as the functions used to replace certs with it seem to overwrite the current option, rather than just adding it alongside. We could just also do that on the MbedTLS side, but I don't know if that'd be a good thing...

> Can you load *multiple* PEMs? You actually *can*(if you look under the MbedTLS hood, loading a directory of PEM files is essentially just loading every PEM directly), so I just added that. As for the `CYTO_TLS_CA`, I'm not sure I can exactly replicate that behavior around LibreSSL, as the functions used to replace certs with it seem to *overwrite* the current option, rather than just adding it alongside. We *could* just also do that on the MbedTLS side, but I don't know if that'd be a good thing...

Ah, that's a bummer. I suppose maybe it would suffice to have CYTO_TLS_CA replace the system's CA store for all implementations. In other words, have Libre and Open check CYTO_TLS_CA and load the store given by that variable if it is set, otherwise do nothing and assume that they load the system store. For Mbed, only check and load the other certificate stores if CYTO_TLS_CA is unset, so that the behavior is consistent across all three implementations: if CYTO_TLS_CA is set, use only that store, otherwise use the system stores, and in the case of Mbed, try to determine what those stores are.

Doe that make sense? Does that sound like a good idea?

Ah, that's a bummer. I suppose maybe it would suffice to have `CYTO_TLS_CA` replace the system's CA store for all implementations. In other words, have Libre and Open check `CYTO_TLS_CA` and load the store given by that variable if it is set, otherwise do nothing and assume that they load the system store. For Mbed, only check and load the other certificate stores if `CYTO_TLS_CA` is unset, so that the behavior is consistent across all three implementations: if `CYTO_TLS_CA` is set, use *only* that store, otherwise use the system stores, and in the case of Mbed, try to determine what those stores are. Doe that make sense? Does that sound like a good idea?
TlsInitClient(int fd, const char *serverName)
{
MbedCookie *cookie;
int err;
if (!serverName)
{
return NULL;
}
cookie = Malloc(sizeof(MbedCookie));
memset(cookie, 0, sizeof(MbedCookie));
cookie->fd = fd;
cookie->serverside = false;
/* Initialise MbedTLS */
mbedtls_net_init(&cookie->serverFD);
mbedtls_ssl_init(&cookie->ssl);
mbedtls_ssl_config_init(&cookie->conf);
mbedtls_x509_crt_init(&cookie->cert);
mbedtls_ctr_drbg_init(&cookie->ctrDrbg);
mbedtls_pk_init(&cookie->serverkey);
mbedtls_entropy_init(&cookie->entropy);
err = mbedtls_ctr_drbg_seed(
&cookie->ctrDrbg,
mbedtls_entropy_func,
&cookie->entropy,
(const unsigned char *) serverName, strlen(serverName)
);
if (err != 0)
{
Log(LOG_ERR, "MbedTLS failure on client init: %d", err);
goto error;
}
cookie->serverFD.fd = fd;
err = mbedtls_ssl_config_defaults(
&cookie->conf,
MBEDTLS_SSL_IS_CLIENT,
MBEDTLS_SSL_TRANSPORT_STREAM,
MBEDTLS_SSL_PRESET_DEFAULT
);
if (err != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on client config: %s", message);
goto error;
}
/* Setup key verification */
if (!RegisterPEMs(&cookie->cert))
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on client certs: %s", message);
goto error;
}
mbedtls_ssl_conf_authmode(&cookie->conf, MBEDTLS_SSL_VERIFY_REQUIRED);
mbedtls_ssl_conf_ca_chain(&cookie->conf, &cookie->cert, NULL);
/* Setup some callbacks */
mbedtls_ssl_conf_rng(
&cookie->conf,
mbedtls_ctr_drbg_random,
&cookie->ctrDrbg
);
if ((err = mbedtls_ssl_setup(&cookie->ssl, &cookie->conf)) != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on SSL setup: %s", message);
goto error;
}
/* Setup some functions */
mbedtls_ssl_set_bio(
&cookie->ssl, &cookie->serverFD,
mbedtls_net_send, mbedtls_net_recv, NULL
);
/* Setup the servername */
if ((err = mbedtls_ssl_set_hostname(&cookie->ssl, serverName)) != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on client hostname: %s", message);
goto error;
}
while ((err = mbedtls_ssl_handshake(&cookie->ssl)) != 0)
{
char message[256];
switch (err)
{
case MBEDTLS_ERR_SSL_WANT_WRITE:
case MBEDTLS_ERR_SSL_WANT_READ:
break;
default:
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on handshake: %s", message);
goto error;
}
}
return cookie;
error:
mbedtls_net_free(&cookie->serverFD);
mbedtls_ssl_free(&cookie->ssl);
mbedtls_ssl_config_free(&cookie->conf);
mbedtls_ctr_drbg_free(&cookie->ctrDrbg);
mbedtls_entropy_free(&cookie->entropy);
Free(cookie);
return NULL;
}
void *
TlsInitServer(int fd, const char *crt, const char *key)
{
MbedCookie *cookie;
char *seed;
int err;
if (!crt || !key)
{
return NULL;
}
cookie = Malloc(sizeof(MbedCookie));
memset(cookie, 0, sizeof(MbedCookie));
cookie->fd = fd;
cookie->serverside = true;
/* Initialise MbedTLS */
mbedtls_net_init(&cookie->serverFD);
mbedtls_ssl_init(&cookie->ssl);
mbedtls_ssl_config_init(&cookie->conf);
mbedtls_x509_crt_init(&cookie->cert);
mbedtls_ctr_drbg_init(&cookie->ctrDrbg);
mbedtls_pk_init(&cookie->serverkey);
mbedtls_entropy_init(&cookie->entropy);
err = mbedtls_ctr_drbg_seed(
&cookie->ctrDrbg,
mbedtls_entropy_func,
&cookie->entropy,
(const unsigned char *) key, strlen(key)
);
if (err != 0)
{
Log(LOG_ERR, "MbedTLS failure on server init: %d", err);
goto error;
}
/* Add a source of entropy if possible(using the CYTO_TLS_SEED env).
* Note that we ignore the error code. */
seed = getenv("CYTO_TLS_SEED");
mbedtls_entropy_update_seed_file(&cookie->entropy, seed);
/* Setup key verification */
if ((err = mbedtls_x509_crt_parse_file(&cookie->cert, crt)) != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on server certs: %s", message);
goto error;
}
if ((err = mbedtls_pk_parse_keyfile(&cookie->serverkey, key, NULL, mbedtls_entropy_func, &cookie->ctrDrbg)) != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on server certs: %s", message);
goto error;
}
mbedtls_ssl_conf_ca_chain(&cookie->conf, cookie->cert.next, NULL);
if ((err = mbedtls_ssl_conf_own_cert(&cookie->conf, &cookie->cert, &cookie->serverkey)) != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on server certs: %s", message);
goto error;
}
/* Setup SSL */
cookie->serverFD.fd = fd;
err = mbedtls_ssl_config_defaults(
&cookie->conf,
MBEDTLS_SSL_IS_SERVER,
MBEDTLS_SSL_TRANSPORT_STREAM,
MBEDTLS_SSL_PRESET_DEFAULT
);
if (err != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on server SSL: %s", message);
goto error;
}
/* Setup some callbacks */
mbedtls_ssl_conf_rng(
&cookie->conf,
mbedtls_ctr_drbg_random,
&cookie->ctrDrbg
);
mbedtls_ssl_conf_ca_chain(&cookie->conf, cookie->cert.next, NULL);
if ((err = mbedtls_ssl_setup(&cookie->ssl, &cookie->conf)) != 0)
{
char message[256];
mbedtls_strerror(err, message, 255);
Log(LOG_ERR, "MbedTLS failure on SSL setup: %s", message);
goto error;
}
/* Client connexion */
/* Setup some functions */
mbedtls_ssl_set_bio(
&cookie->ssl, &cookie->serverFD,
mbedtls_net_send, mbedtls_net_recv, NULL
);
/* Handshake the client */
while ((err = mbedtls_ssl_handshake(&cookie->ssl)) != 0)
{
switch (err)
{
case MBEDTLS_ERR_SSL_WANT_WRITE:
case MBEDTLS_ERR_SSL_WANT_READ:
break;
default:
goto error;
}
}
return cookie;
error:
mbedtls_net_free(&cookie->serverFD);
mbedtls_ssl_free(&cookie->ssl);
mbedtls_ssl_config_free(&cookie->conf);
mbedtls_ctr_drbg_free(&cookie->ctrDrbg);
mbedtls_entropy_free(&cookie->entropy);
Free(cookie);
return NULL;
}
ssize_t
TlsRead(void *cookie, void *buf, size_t nBytes)
{
MbedCookie *cooked = cookie;
int ret;
if (!cookie || !buf)
{
return -1;
}
ret = mbedtls_ssl_read(&cooked->ssl, buf, nBytes);
if (ret <= 0)
{
ret = -1;
}
return ret;
}
ssize_t
TlsWrite(void *cookie, void *buf, size_t nBytes)
{
MbedCookie *cooked = cookie;
int ret;
if (!cookie || !buf)
{
return -1;
}
ret = mbedtls_ssl_write(&cooked->ssl, buf, nBytes);
if (ret <= 0)
{
ret = -1;
}
return ret;
}
int
TlsClose(void *cookie)
{
MbedCookie *cooked = cookie;
if (!cookie)
{
return -1;
}
mbedtls_net_free(&cooked->serverFD);
mbedtls_ssl_free(&cooked->ssl);
mbedtls_ssl_config_free(&cooked->conf);
mbedtls_ctr_drbg_free(&cooked->ctrDrbg);
mbedtls_entropy_free(&cooked->entropy);
mbedtls_x509_crt_free(&cooked->cert);
if (cooked->serverside)
{
mbedtls_pk_free(&cooked->serverkey);
}
Free(cooked);
return 0;
}
#endif

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@ -399,7 +399,7 @@ end_loop:
}
else if (StrEquals(op, "def?"))
{
Definition *def;
Definition *def = NULL;
size_t i;
char *directive = Eval(&argv, stack);