@@ -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 username/password from envp string array */
+ const char *username = get_env("username", envp);
+ const char *password = get_env("password", envp);
- /* get auth_control_file filename from envp string array*/
- const char *auth_control_file = get_env("auth_control_file", envp);
+ /* get auth_control_file filename from envp string array*/
+ const char *auth_control_file = get_env("auth_control_file", envp);
- printf("DEFER u='%s' p='%s' acf='%s'\n",
+ 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;
- }
+ /* Authenticate asynchronously in n seconds */
+ if (!auth_control_file)
+ {
+ return OPENVPN_PLUGIN_FUNC_ERROR;
}
- else
+
+ /* 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_SUCCESS;
+ 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 (!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)
{
- if (!pcc->generated_pf_file)
+ 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)
{
- 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;
- }
+ plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "error reading '%s'", buf);
+ close(r_fd);
+ close(w_fd);
+ exit(0);
}
- else
+ int w = write(w_fd, data, r);
+ if (w < 0 || w != r)
{
- return OPENVPN_PLUGIN_FUNC_ERROR;
+ plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "error writing %d bytes to '%s'", r, pff);
+ close(r_fd);
+ close(w_fd);
+ exit(0);
}
}
- else
- {
- return OPENVPN_PLUGIN_FUNC_SUCCESS;
- }
+ 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)
- {
- return OPENVPN_PLUGIN_FUNC_SUCCESS;
- }
- else
+ 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_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);
}
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> --- sample/sample-plugins/defer/simple.c | 357 ++++++++++++++++++++------- 1 file changed, 265 insertions(+), 92 deletions(-)