mirror/openvpn
0
0
Fork 0
mirror of https://github.com/OpenVPN/openvpn.git synced 2024-09-19 19:42:30 +02:00
Code

clean up / rewrite sample-plugins/defer/simple.c

Browse Source 
If we ship something that we consider a form of documentation
"this is how to write an OpenVPN plugin" it should meet our standards
for secure and modern code.  This plugin did neither.

  - get rid of system() calls, especially those that enabled a
    remote-root exploit if this code was used "as is"

  - change logging from printf() to OpenVPN's plugin_log()

  - this requires changing to openvpn_plugin_open_v3() to get
    to the function pointers

  - change wacky "background and sleep in the shell call" to the
    double-fork/waitpid model we use in plugins/auth-pam
    (copy-paste code reuse)

  - OpenVPN 2.5 and later react badly to OPENVPN_PLUGIN_FUNC_ERROR
    returns to OPENVPN_PLUGIN_ENABLE_PF calls (SIGSEGV crash), so
    always return SUCCESS.  Only hook ENABLE_PF if that functionality
    is actually requested ("setenv test_packet_filter NN").

  - change deeply-nested functions auth_user_pass_verify() and
    tls_final() to use early-return style

  - actually make defered PF setup *work* with recent OpenVPNs
    (pre-creating temp files broke this, so unlink() the pre-created
    file in the ENABLE_PF hook, and re-create asyncronously later)

  - add lots of comments explaining why we do things this way

Security issue reported by "oxr463" on HackerOne.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20210121172536.32500-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21466.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
This commit is contained in:
Gert Doering 2021-01-21 18:25:36 +01:00
parent 6a0c51baaa
commit 452e016cba
1 changed files with 269 additions and 96 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

365
sample/sample-plugins/defer/simple.c
View File

@ -54,13 +54,16 @@
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/wait.h>
#include "openvpn-plugin.h"
/* bool definitions */
#define bool int
#define true 1
#define false 0
/* Pointers to functions exported from openvpn */
static plugin_log_t plugin_log = NULL;
/*
* Our context, where we keep our state.
@ -76,6 +79,9 @@ struct plugin_per_client_context {
bool generated_pf_file;
};
/* module name for plugin_log() */
static char *MODULE = "defer/simple";
/*
* Given an environmental variable name, search
* the envp array for its value, returning it
@ -130,33 +136,46 @@ atoi_null0(const char *str)
}
}
OPENVPN_EXPORT openvpn_plugin_handle_t
openvpn_plugin_open_v1(unsigned int *type_mask, const char *argv[], const char *envp[])
/* use v3 functions so we can use openvpn's logging and base64 etc. */
OPENVPN_EXPORT int
openvpn_plugin_open_v3(const int v3structver,
struct openvpn_plugin_args_open_in const *args,
struct openvpn_plugin_args_open_return *ret)
{
const char **envp = args->envp; /* environment variables */
struct plugin_context *context;
printf("FUNC: openvpn_plugin_open_v1\n");
/* Check API compatibility -- struct version 5 or higher needed */
if (v3structver < 5)
{
fprintf(stderr, "sample-client-connect: this plugin is incompatible with the running version of OpenVPN\n");
return OPENVPN_PLUGIN_FUNC_ERROR;
}
/* Save global pointers to functions exported from openvpn */
plugin_log = args->callbacks->plugin_log;
plugin_log(PLOG_NOTE, MODULE, "FUNC: openvpn_plugin_open_v3");
/*
* Allocate our context
*/
context = (struct plugin_context *) calloc(1, sizeof(struct plugin_context));
if (context == NULL)
if (!context)
{
printf("PLUGIN: allocating memory for context failed\n");
return NULL;
goto error;
}
context->test_deferred_auth = atoi_null0(get_env("test_deferred_auth", envp));
printf("TEST_DEFERRED_AUTH %d\n", context->test_deferred_auth);
plugin_log(PLOG_NOTE, MODULE, "TEST_DEFERRED_AUTH %d", context->test_deferred_auth);
context->test_packet_filter = atoi_null0(get_env("test_packet_filter", envp));
printf("TEST_PACKET_FILTER %d\n", context->test_packet_filter);
plugin_log(PLOG_NOTE, MODULE, "TEST_PACKET_FILTER %d", context->test_packet_filter);
/*
* Which callbacks to intercept.
*/
*type_mask =
ret->type_mask =
OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_UP)
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_DOWN)
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_ROUTE_UP)
@ -166,90 +185,241 @@ openvpn_plugin_open_v1(unsigned int *type_mask, const char *argv[], const char *
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_CLIENT_CONNECT_V2)
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_CLIENT_DISCONNECT)
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_LEARN_ADDRESS)
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_TLS_FINAL)
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_ENABLE_PF);
|OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_TLS_FINAL);
return (openvpn_plugin_handle_t) context;
/* ENABLE_PF should only be called if we're actually willing to do PF */
if (context->test_packet_filter)
{
ret->type_mask |= OPENVPN_PLUGIN_MASK(OPENVPN_PLUGIN_ENABLE_PF);
}
ret->handle = (openvpn_plugin_handle_t *) context;
plugin_log(PLOG_NOTE, MODULE, "initialization succeeded");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
error:
if (context)
{
free(context);
}
plugin_log(PLOG_NOTE, MODULE, "initialization failed");
return OPENVPN_PLUGIN_FUNC_ERROR;
}
static int
auth_user_pass_verify(struct plugin_context *context, struct plugin_per_client_context *pcc, const char *argv[], const char *envp[])
auth_user_pass_verify(struct plugin_context *context,
struct plugin_per_client_context *pcc,
const char *argv[], const char *envp[])
{
if (context->test_deferred_auth)
if (!context->test_deferred_auth)
{
/* get username/password from envp string array */
const char *username = get_env("username", envp);
const char *password = get_env("password", envp);
return OPENVPN_PLUGIN_FUNC_SUCCESS;
}
/* get auth_control_file filename from envp string array*/
const char *auth_control_file = get_env("auth_control_file", envp);
/* get username/password from envp string array */
const char *username = get_env("username", envp);
const char *password = get_env("password", envp);
printf("DEFER u='%s' p='%s' acf='%s'\n",
/* get auth_control_file filename from envp string array*/
const char *auth_control_file = get_env("auth_control_file", envp);
plugin_log(PLOG_NOTE, MODULE, "DEFER u='%s' p='%s' acf='%s'",
np(username),
np(password),
np(auth_control_file));
/* Authenticate asynchronously in n seconds */
if (auth_control_file)
{
char buf[256];
int auth = 2;
sscanf(username, "%d", &auth);
snprintf(buf, sizeof(buf), "( sleep %d ; echo AUTH %s %d ; echo %d >%s ) &",
context->test_deferred_auth,
auth_control_file,
auth,
pcc->n_calls < auth,
auth_control_file);
printf("%s\n", buf);
system(buf);
pcc->n_calls++;
return OPENVPN_PLUGIN_FUNC_DEFERRED;
}
else
{
return OPENVPN_PLUGIN_FUNC_ERROR;
}
}
else
/* Authenticate asynchronously in n seconds */
if (!auth_control_file)
{
return OPENVPN_PLUGIN_FUNC_SUCCESS;
return OPENVPN_PLUGIN_FUNC_ERROR;
}
/* we do not want to complicate our lives with having to wait()
* for child processes (so they are not zombiefied) *and* we MUST NOT
* fiddle with signal handlers (= shared with openvpn main), so
* we use double-fork() trick.
*/
/* fork, sleep, succeed (no "real" auth done = always succeed) */
pid_t p1 = fork();
if (p1 < 0) /* Fork failed */
{
return OPENVPN_PLUGIN_FUNC_ERROR;
}
if (p1 > 0) /* parent process */
{
waitpid(p1, NULL, 0);
return OPENVPN_PLUGIN_FUNC_DEFERRED;
}
/* first gen child process, fork() again and exit() right away */
pid_t p2 = fork();
if (p2 < 0)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "BACKGROUND: fork(2) failed");
exit(1);
}
if (p2 != 0) /* new parent: exit right away */
{
exit(0);
}
/* (grand-)child process
* - never call "return" now (would mess up openvpn)
* - return status is communicated by file
* - then exit()
*/
/* do mighty complicated work that will really take time here... */
plugin_log(PLOG_NOTE, MODULE, "in async/deferred handler, sleep(%d)", context->test_deferred_auth);
sleep(context->test_deferred_auth);
/* now signal success state to openvpn */
int fd = open(auth_control_file, O_WRONLY);
if (fd < 0)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "open('%s') failed", auth_control_file);
exit(1);
}
plugin_log(PLOG_NOTE, MODULE, "auth_user_pass_verify: done" );
if (write(fd, "1", 1) != 1)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "write to '%s' failed", auth_control_file );
}
close(fd);
exit(0);
}
static int
tls_final(struct plugin_context *context, struct plugin_per_client_context *pcc, const char *argv[], const char *envp[])
{
if (context->test_packet_filter)
{
if (!pcc->generated_pf_file)
{
const char *pff = get_env("pf_file", envp);
const char *cn = get_env("username", envp);
if (pff && cn)
{
char buf[256];
snprintf(buf, sizeof(buf), "( sleep %d ; echo PF %s/%s ; cp \"%s.pf\" \"%s\" ) &",
context->test_packet_filter, cn, pff, cn, pff);
printf("%s\n", buf);
system(buf);
pcc->generated_pf_file = true;
return OPENVPN_PLUGIN_FUNC_SUCCESS;
}
else
{
return OPENVPN_PLUGIN_FUNC_ERROR;
}
}
else
{
return OPENVPN_PLUGIN_FUNC_ERROR;
}
}
else
if (!context->test_packet_filter) /* no PF testing, nothing to do */
{
return OPENVPN_PLUGIN_FUNC_SUCCESS;
}
if (pcc->generated_pf_file) /* we already have created a file */
{
return OPENVPN_PLUGIN_FUNC_ERROR;
}
const char *pff = get_env("pf_file", envp);
const char *cn = get_env("username", envp);
if (!pff || !cn) /* required vars missing */
{
return OPENVPN_PLUGIN_FUNC_ERROR;
}
pcc->generated_pf_file = true;
/* the PF API is, basically
* - OpenVPN sends a filename (pf_file) to the plugin
* - OpenVPN main loop will check every second if that file shows up
* - when it does, it will be read & used for the pf config
* the pre-created file needs to be removed in ...ENABLE_PF
* to make deferred PF setup work
*
* the regular PF hook does not know the client username or CN, so
* this is deferred to the TLS_FINAL hook which knows these things
*/
/* do the double fork dance (see above for more verbose comments)
*/
pid_t p1 = fork();
if (p1 < 0) /* Fork failed */
{
return OPENVPN_PLUGIN_FUNC_ERROR;
}
if (p1 > 0) /* parent process */
{
waitpid(p1, NULL, 0);
return OPENVPN_PLUGIN_FUNC_SUCCESS; /* no _DEFERRED here! */
}
/* first gen child process, fork() again and exit() right away */
pid_t p2 = fork();
if (p2 < 0)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "BACKGROUND: fork(2) failed");
exit(1);
}
if (p2 != 0) /* new parent: exit right away */
{
exit(0);
}
/* (grand-)child process
* - never call "return" now (would mess up openvpn)
* - return status is communicated by file
* - then exit()
*/
/* at this point, the plugin can take its time, because OpenVPN will
* no longer block waiting for the call to finish
*
* in this example, we build a PF file by copying over a file
* named "<username>.pf" to the OpenVPN-provided pf file name
*
* a real example could do a LDAP lookup, a REST call, ...
*/
plugin_log(PLOG_NOTE, MODULE, "in async/deferred tls_final handler, sleep(%d)", context->test_packet_filter);
sleep(context->test_packet_filter);
char buf[256];
snprintf(buf, sizeof(buf), "%s.pf", cn );
/* there is a small race condition here - OpenVPN could detect our
* file while we have only written half of it. So "perfect" code
* needs to create this with a temp file name, and then rename() it
* after it has been written. But I am lazy.
*/
int w_fd = open( pff, O_WRONLY|O_CREAT, 0600 );
if (w_fd < 0)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "can't write to '%s'", pff);
exit(0);
}
int r_fd = open( buf, O_RDONLY );
if (r_fd < 0)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "can't read '%s', creating empty pf file", buf);
close(w_fd);
exit(0);
}
char data[1024];
int r;
do
{
r = read(r_fd, data, sizeof(data));
if (r < 0)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "error reading '%s'", buf);
close(r_fd);
close(w_fd);
exit(0);
}
int w = write(w_fd, data, r);
if (w < 0 || w != r)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "error writing %d bytes to '%s'", r, pff);
close(r_fd);
close(w_fd);
exit(0);
}
}
while(r > 0);
plugin_log(PLOG_NOTE, MODULE, "copied PF config from '%s' to '%s', job done", buf, pff);
exit(0);
}
OPENVPN_EXPORT int
@ -265,58 +435,61 @@ openvpn_plugin_func_v2(openvpn_plugin_handle_t handle,
switch (type)
{
case OPENVPN_PLUGIN_UP:
printf("OPENVPN_PLUGIN_UP\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_UP");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_DOWN:
printf("OPENVPN_PLUGIN_DOWN\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_DOWN");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_ROUTE_UP:
printf("OPENVPN_PLUGIN_ROUTE_UP\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_ROUTE_UP");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_IPCHANGE:
printf("OPENVPN_PLUGIN_IPCHANGE\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_IPCHANGE");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_TLS_VERIFY:
printf("OPENVPN_PLUGIN_TLS_VERIFY\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_TLS_VERIFY");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY:
printf("OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_AUTH_USER_PASS_VERIFY");
return auth_user_pass_verify(context, pcc, argv, envp);
case OPENVPN_PLUGIN_CLIENT_CONNECT_V2:
printf("OPENVPN_PLUGIN_CLIENT_CONNECT_V2\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_CLIENT_CONNECT_V2");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_CLIENT_DISCONNECT:
printf("OPENVPN_PLUGIN_CLIENT_DISCONNECT\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_CLIENT_DISCONNECT");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_LEARN_ADDRESS:
printf("OPENVPN_PLUGIN_LEARN_ADDRESS\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_LEARN_ADDRESS");
return OPENVPN_PLUGIN_FUNC_SUCCESS;
case OPENVPN_PLUGIN_TLS_FINAL:
printf("OPENVPN_PLUGIN_TLS_FINAL\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_TLS_FINAL");
return tls_final(context, pcc, argv, envp);
case OPENVPN_PLUGIN_ENABLE_PF:
printf("OPENVPN_PLUGIN_ENABLE_PF\n");
if (context->test_packet_filter)
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_ENABLE_PF");
/* OpenVPN pre-creates the file, which gets in the way of
* deferred pf setup - so remove it here, and re-create
* it in the background handler (in tls_final()) when ready
*/
const char *pff = get_env("pf_file", envp);
if (pff)
{
return OPENVPN_PLUGIN_FUNC_SUCCESS;
}
else
{
return OPENVPN_PLUGIN_FUNC_ERROR;
(void) unlink(pff);
}
return OPENVPN_PLUGIN_FUNC_SUCCESS; /* must succeed */
default:
printf("OPENVPN_PLUGIN_?\n");
plugin_log(PLOG_NOTE, MODULE, "OPENVPN_PLUGIN_?");
return OPENVPN_PLUGIN_FUNC_ERROR;
}
}
@ -324,14 +497,14 @@ openvpn_plugin_func_v2(openvpn_plugin_handle_t handle,
OPENVPN_EXPORT void *
openvpn_plugin_client_constructor_v1(openvpn_plugin_handle_t handle)
{
printf("FUNC: openvpn_plugin_client_constructor_v1\n");
plugin_log(PLOG_NOTE, MODULE, "FUNC: openvpn_plugin_client_constructor_v1");
return calloc(1, sizeof(struct plugin_per_client_context));
}
OPENVPN_EXPORT void
openvpn_plugin_client_destructor_v1(openvpn_plugin_handle_t handle, void *per_client_context)
{
printf("FUNC: openvpn_plugin_client_destructor_v1\n");
plugin_log(PLOG_NOTE, MODULE, "FUNC: openvpn_plugin_client_destructor_v1");
free(per_client_context);
}
@ -339,6 +512,6 @@ OPENVPN_EXPORT void
openvpn_plugin_close_v1(openvpn_plugin_handle_t handle)
{
struct plugin_context *context = (struct plugin_context *) handle;
printf("FUNC: openvpn_plugin_close_v1\n");
plugin_log(PLOG_NOTE, MODULE, "FUNC: openvpn_plugin_close_v1");
free(context);
}