notify: add new --uid= command

The new --uid= switch allows selecting the UID from which the
notificaiton messages shall originate.

This is primarily useful for testing purposes, but might have other
uses.

1 files changed, 36 insertions, 2 deletions

diff --git a/src/notify/notify.c b/src/notify/notify.c
index 4a34e1e9db..d58a45cdd2 100644
--- a/src/notify/notify.c
+++ b/src/notify/notify.c
@@ -33,12 +33,15 @@
 #include "parse-util.h"
 #include "string-util.h"
 #include "strv.h"
+#include "user-util.h"
 #include "util.h"
 
 static bool arg_ready = false;
 static pid_t arg_pid = 0;
 static const char *arg_status = NULL;
 static bool arg_booted = false;
+static uid_t arg_uid = UID_INVALID;
+static gid_t arg_gid = GID_INVALID;
 
 static void help(void) {
         printf("%s [OPTIONS...] [VARIABLE=VALUE...]\n\n"
@@ -46,7 +49,8 @@ static void help(void) {
                "  -h --help            Show this help\n"
                "     --version         Show package version\n"
                "     --ready           Inform the init system about service start-up completion\n"
-               "     --pid[=PID]       Set main pid of daemon\n"
+               "     --pid[=PID]       Set main PID of daemon\n"
+               "     --uid=USER        Set user to send from\n"
                "     --status=TEXT     Set status text\n"
                "     --booted          Check if the system was booted up with systemd\n",
                program_invocation_short_name);
@@ -60,6 +64,7 @@ static int parse_argv(int argc, char *argv[]) {
                 ARG_PID,
                 ARG_STATUS,
                 ARG_BOOTED,
+                ARG_UID,
         };
 
         static const struct option options[] = {
@@ -69,10 +74,11 @@ static int parse_argv(int argc, char *argv[]) {
                 { "pid",       optional_argument, NULL, ARG_PID       },
                 { "status",    required_argument, NULL, ARG_STATUS    },
                 { "booted",    no_argument,       NULL, ARG_BOOTED    },
+                { "uid",       required_argument, NULL, ARG_UID       },
                 {}
         };
 
-        int c;
+        int c, r;
 
         assert(argc >= 0);
         assert(argv);
@@ -112,6 +118,18 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_booted = true;
                         break;
 
+                case ARG_UID: {
+                        const char *u = optarg;
+
+                        r = get_user_creds(&u, &arg_uid, &arg_gid, NULL, NULL);
+                        if (r == -ESRCH) /* If the user doesn't exist, then accept it anyway as numeric */
+                                r = parse_uid(u, &arg_uid);
+                        if (r < 0)
+                                return log_error_errno(r, "Can't resolve user %s: %m", optarg);
+
+                        break;
+                }
+
                 case '?':
                         return -EINVAL;
 
@@ -190,6 +208,22 @@ int main(int argc, char* argv[]) {
                 goto finish;
         }
 
+        /* If this is requested change to the requested UID/GID. Note thta we only change the real UID here, and leave
+           the effective UID in effect (which is 0 for this to work). That's because we want the privileges to fake the
+           ucred data, and sd_pid_notify() uses the real UID for filling in ucred. */
+
+        if (arg_gid != GID_INVALID)
+                if (setregid(arg_gid, (gid_t) -1) < 0) {
+                        r = log_error_errno(errno, "Failed to change GID: %m");
+                        goto finish;
+                }
+
+        if (arg_uid != UID_INVALID)
+                if (setreuid(arg_uid, (uid_t) -1) < 0) {
+                        r = log_error_errno(errno, "Failed to change UID: %m");
+                        goto finish;
+                }
+
         r = sd_pid_notify(arg_pid ? arg_pid : getppid(), false, n);
         if (r < 0) {
                 log_error_errno(r, "Failed to notify init system: %m");