If OpenVPN signals deferred authentication support (by setting
the internal environment variables "auth_control_file" and
"deferred_auth_pam"), do not wait for PAM stack to finish. Instead,
the privileged PAM process returns RESPONSE_DEFER via the control
socket, which gets turned into OPENVPN_PLUGIN_FUNC_DEFERRED towards
openvpn.
The PAM process will then fork() and handle all the PAM auth in
the new process, signalling success/failure back by means of the
auth_control_file (forking twice, to simplify wait() handling).
With the extra fork(), multiple deferred authentications can run at
the same time - otherwise the first one would block the next auth
call (because the child would not be ready again to read from the
control socket).
Lightly tested on Linux.
Signed-off-by: Gert Doering <g...@greenie.muc.de>
--
v2:
- only do deferred auth if "deferred_auth_pam" is set (env)
- put deferred auth logic into do_deferred_pam_auth()
- line-wrap lines where needed
- close "background end" of socketpair in deferred auth process
- remove leftover /* plugin_log() */ lines from initial testing
- tested over a few hundred "15s delayed" authentication cycles
---
src/plugins/auth-pam/auth-pam.c | 124 +++++++++++++++++++++++++++++++-
1 file changed, 122 insertions(+), 2 deletions(-)
diff --git a/src/plugins/auth-pam/auth-pam.c b/src/plugins/auth-pam/auth-pam.c
index 9a11876d..2a75e5f0 100644
--- a/src/plugins/auth-pam/auth-pam.c
+++ b/src/plugins/auth-pam/auth-pam.c
@@ -62,6 +62,7 @@
#define RESPONSE_INIT_FAILED 11
#define RESPONSE_VERIFY_SUCCEEDED 12
#define RESPONSE_VERIFY_FAILED 13
+#define RESPONSE_DEFER 14
/* Pointers to functions exported from openvpn */
static plugin_log_t plugin_log = NULL;
@@ -524,12 +525,31 @@ openvpn_plugin_func_v1(openvpn_plugin_handle_t handle,
const int type, const cha
const char *password = get_env("password", envp);
const char *common_name = get_env("common_name", envp) ?
get_env("common_name", envp) : "";
+ /* should we do deferred auth?
+ * yes, if there is "auth_control_file" and "deferred_auth_pam" env
+ */
+ const char *auth_control_file = get_env("auth_control_file", envp);
+ const char *deferred_auth_pam = get_env("deferred_auth_pam", envp);
+ if ( auth_control_file != NULL && deferred_auth_pam != NULL)
+ {
+ if (DEBUG(context->verb))
+ {
+ plugin_log(PLOG_NOTE, MODULE, "do deferred auth '%s'",
+ auth_control_file);
+ }
+ }
+ else
+ {
+ auth_control_file = "";
+ }
+
if (username && strlen(username) > 0 && password)
{
if (send_control(context->foreground_fd, COMMAND_VERIFY) == -1
|| send_string(context->foreground_fd, username) == -1
|| send_string(context->foreground_fd, password) == -1
- || send_string(context->foreground_fd, common_name) == -1)
+ || send_string(context->foreground_fd, common_name) == -1
+ || send_string(context->foreground_fd, auth_control_file) ==
-1)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "Error sending auth
info to background process");
}
@@ -540,6 +560,14 @@ openvpn_plugin_func_v1(openvpn_plugin_handle_t handle,
const int type, const cha
{
return OPENVPN_PLUGIN_FUNC_SUCCESS;
}
+ if (status == RESPONSE_DEFER)
+ {
+ if (DEBUG(context->verb))
+ {
+ plugin_log(PLOG_NOTE, MODULE, "deferred
authentication");
+ }
+ return OPENVPN_PLUGIN_FUNC_DEFERRED;
+ }
if (status == -1)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "Error receiving
auth confirmation from background process");
@@ -782,6 +810,80 @@ pam_auth(const char *service, const struct user_pass *up)
return ret;
}
+/*
+ * deferred auth handler
+ * - fork() (twice, to avoid the need for async wait / SIGCHLD handling)
+ * - query PAM stack via pam_auth()
+ * - send response back to OpenVPN via "ac_file_name"
+ *
+ * parent process returns "0" for "fork() and wait() succeeded",
+ * "-1" for "something went wrong, abort program"
+ */
+
+static int
+do_deferred_pam_auth(int fd, const char *ac_file_name,
+ const char *service, const struct user_pass *up)
+{
+ if (send_control(fd, RESPONSE_DEFER) == -1)
+ {
+ plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "BACKGROUND: write error on
response socket [4]");
+ return -1;
+ }
+
+ /* double forking so we do not need to wait() for async auth kids */
+ pid_t p1 = fork();
+
+ if ( p1 < 0 )
+ {
+ plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "BACKGROUND: fork(1) failed");
+ return -1;
+ }
+ if ( p1 != 0 ) /* parent */
+ {
+ waitpid(p1, NULL, 0);
+ return 0; /* parent's job succeeded */
+ }
+
+ /* child */
+ close(fd); /* socketpair no longer needed */
+
+ 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);
+ }
+
+ /* grandchild */
+ plugin_log(PLOG_NOTE, MODULE, "BACKGROUND: deferred auth for '%s', pid=%d",
+ up->username, (int) getpid() );
+
+ /* the rest is very simple: do PAM, write status byte to file, done */
+ int ac_fd = open( ac_file_name, O_WRONLY );
+ if ( ac_fd < 0 )
+ {
+ plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "cannot open '%s' for writing",
+ ac_file_name );
+ exit(1);
+ }
+ int pam_success = pam_auth(service, up);
+
+ if ( write( ac_fd, pam_success? "1": "0", 1 ) != 1 )
+ {
+ plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "cannot write to '%s'",
+ ac_file_name );
+ }
+ close(ac_fd);
+ plugin_log(PLOG_NOTE, MODULE, "BACKGROUND: %s: deferred auth: PAM %s",
+ up->username, pam_success? "succeeded": "rejected" );
+ exit(0);
+}
+
/*
* Background process -- runs with privilege.
*/
@@ -789,6 +891,7 @@ static void
pam_server(int fd, const char *service, int verb, const struct name_value_list
*name_value_list)
{
struct user_pass up;
+ char ac_file_name[PATH_MAX];
int command;
#ifdef USE_PAM_DLOPEN
static const char pam_so[] = "libpam.so";
@@ -847,7 +950,8 @@ pam_server(int fd, const char *service, int verb, const
struct name_value_list *
case COMMAND_VERIFY:
if (recv_string(fd, up.username, sizeof(up.username)) == -1
|| recv_string(fd, up.password, sizeof(up.password)) == -1
- || recv_string(fd, up.common_name, sizeof(up.common_name))
== -1)
+ || recv_string(fd, up.common_name, sizeof(up.common_name))
== -1
+ || recv_string(fd, ac_file_name, sizeof(ac_file_name)) ==
-1)
{
plugin_log(PLOG_ERR|PLOG_ERRNO, MODULE, "BACKGROUND: read
error on command channel: code=%d, exiting",
command);
@@ -867,6 +971,22 @@ pam_server(int fd, const char *service, int verb, const
struct name_value_list *
/* If password is of the form SCRV1:base64:base64 split it up
*/
split_scrv1_password(&up);
+ /* client wants deferred auth
+ */
+ if ( strlen(ac_file_name) > 0 )
+ {
+ if (do_deferred_pam_auth(fd, ac_file_name,
+ service, &up) < 0)
+ {
+ goto done;
+ }
+ break;
+ }
+
+
+ /* non-deferred auth: wait for pam result and send
+ * result back via control socketpair
+ */
if (pam_auth(service, &up)) /* Succeeded */
{
if (send_control(fd, RESPONSE_VERIFY_SUCCEEDED) == -1)
--
2.26.2
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