From 18f3bad3ba1ffc5a363d188da8b0653f9b527a18 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 5 Jan 2018 13:26:38 +0100
Subject: [PATCH] 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.

(cherry picked from commit 65c6b99094580afa186199d8091cd7536900526c)

Related: #1663143
---
 man/systemd-notify.xml |  9 +++++++++
 src/notify/notify.c    | 39 ++++++++++++++++++++++++++++++++++++---
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/man/systemd-notify.xml b/man/systemd-notify.xml
index 46ede1ab8f..4048783611 100644
--- a/man/systemd-notify.xml
+++ b/man/systemd-notify.xml
@@ -106,6 +106,15 @@
         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>--uid=</option><replaceable>USER</replaceable></term>
+
+        <listitem><para>Set the user ID to send the notification from. Takes a UNIX user name or numeric UID. When
+        specified the notification message will be sent with the specified UID as sender, in place of the user the
+        command was invoked as. This option requires sufficient privileges in order to be able manipulate the user
+        identity of the process.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><option>--status=</option></term>
 
diff --git a/src/notify/notify.c b/src/notify/notify.c
index 0d382992a5..659ba7c54b 100644
--- a/src/notify/notify.c
+++ b/src/notify/notify.c
@@ -40,6 +40,8 @@ static pid_t arg_pid = 0;
 static const char *arg_status = NULL;
 static bool arg_booted = false;
 static const char *arg_readahead = NULL;
+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"
@@ -47,7 +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"
                "     --readahead=ACTION Controls read-ahead operations\n",
@@ -62,7 +65,8 @@ static int parse_argv(int argc, char *argv[]) {
                 ARG_PID,
                 ARG_STATUS,
                 ARG_BOOTED,
-                ARG_READAHEAD
+                ARG_READAHEAD,
+                ARG_UID,
         };
 
         static const struct option options[] = {
@@ -73,10 +77,11 @@ static int parse_argv(int argc, char *argv[]) {
                 { "status",    required_argument, NULL, ARG_STATUS    },
                 { "booted",    no_argument,       NULL, ARG_BOOTED    },
                 { "readahead", required_argument, NULL, ARG_READAHEAD },
+                { "uid",       required_argument, NULL, ARG_UID       },
                 {}
         };
 
-        int c;
+        int c, r;
 
         assert(argc >= 0);
         assert(argv);
@@ -122,6 +127,18 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_readahead = optarg;
                         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;
 
@@ -209,6 +226,22 @@ 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");