From 0e441354f830f86ff80dab9337fc5bdc033cf687 Mon Sep 17 00:00:00 2001
From: Florian Forster <octo@leeloo.lan.home.verplant.org>
Date: Mon, 3 Sep 2007 15:59:08 +0200
Subject: [PATCH] exec plugin: Set the real group, effective group, and real
 and effective user.

In that order. The manpage and the config template have been updated.
---
 src/collectd-exec.pod |  4 ++--
 src/collectd.conf.in  |  2 +-
 src/collectd.conf.pod | 12 +++++++++---
 src/exec.c            | 34 +++++++++++++++++++++++++---------
 4 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/src/collectd-exec.pod b/src/collectd-exec.pod
index eaa4f8b4..27d0eedc 100644
--- a/src/collectd-exec.pod
+++ b/src/collectd-exec.pod
@@ -8,8 +8,8 @@ collectd-exec - Documentation of collectd's C<exec plugin>
   LoadPlugin exec
   # ...
   <Plugin exec>
-    Exec myuser myprog
-    Exec otheruser /path/to/another/binary
+    Exec "myuser:mygroup" "myprog"
+    Exec "otheruser" "/path/to/another/binary"
   </Plugin>
 
 =head1 DESCRIPTION
diff --git a/src/collectd.conf.in b/src/collectd.conf.in
index 313fd914..af2db91a 100644
--- a/src/collectd.conf.in
+++ b/src/collectd.conf.in
@@ -93,7 +93,7 @@
 #</Plugin>
 
 #<Plugin exec>
-#	Exec user "/path/to/exec"
+#	Exec "user:group" "/path/to/exec"
 #</Plugin>
 
 #<Plugin hddtemp>
diff --git a/src/collectd.conf.pod b/src/collectd.conf.pod
index 3de2f243..29e26af4 100644
--- a/src/collectd.conf.pod
+++ b/src/collectd.conf.pod
@@ -249,9 +249,15 @@ output that is expected from it.
 =item B<Exec> I<User>[:[I<Group>]] I<Executable>
 
 Execute the executable I<Executable> as user I<User>. If the user name is
-followed by a colon and a group name, the program is executed as the specified
-group. If only the colon follows the user name the group defaults to the
-user's login group.
+followed by a colon and a group name, the effective group is set to that group.
+The real group and saved-set group will be set to the default group of that
+user. If no group is given the effective group ID will be the same as the real
+group ID.
+
+Please note that in order to change the user and/or group the daemon needs
+superuser privileges. If the daemon is run as an unprivileged user you must
+specify the same user/group here. If the daemon is run with superuser
+privileges, you must supply a non-root user here.
 
 =back
 
diff --git a/src/exec.c b/src/exec.c
index e899a1c3..d9f2d8ce 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -118,6 +118,7 @@ static void exec_child (program_list_t *pl)
   int status;
   int uid;
   int gid;
+  int egid;
   char *arg0;
 
   struct passwd *sp_ptr;
@@ -140,12 +141,16 @@ static void exec_child (program_list_t *pl)
   }
 
   uid = sp.pw_uid;
+  gid = sp.pw_gid;
   if (uid == 0)
   {
     ERROR ("exec plugin: Cowardly refusing to exec program as root.");
     exit (-1);
   }
 
+  /* The group configured in the configfile is set as effective group, because
+   * this way the forked process can (re-)gain the user's primary group. */
+  egid = -1;
   if (NULL != pl->group)
   {
     if ('\0' != *pl->group) {
@@ -165,27 +170,38 @@ static void exec_child (program_list_t *pl)
 	exit (-1);
       }
 
-      gid = gr.gr_gid;
+      egid = gr.gr_gid;
     }
     else
     {
-      gid = sp.pw_gid;
+      egid = gid;
     }
+  } /* if (pl->group == NULL) */
+
+  status = setgid (gid);
+  if (status != 0)
+  {
+    ERROR ("exec plugin: setgid (%i) failed: %s",
+	gid, sstrerror (errno, errbuf, sizeof (errbuf)));
+    exit (-1);
+  }
 
-    status = setgid (gid);
-    if (0 != status)
+  if (egid != -1)
+  {
+    status = setegid (egid);
+    if (status != 0)
     {
-      ERROR ("exec plugin: setgid failed: %s",
-	  sstrerror (errno, errbuf, sizeof (errbuf)));
+      ERROR ("exec plugin: setegid (%i) failed: %s",
+	  egid, sstrerror (errno, errbuf, sizeof (errbuf)));
       exit (-1);
     }
-  } /* if (pl->group == NULL) */
+  }
 
   status = setuid (uid);
   if (status != 0)
   {
-    ERROR ("exec plugin: setuid failed: %s",
-	sstrerror (errno, errbuf, sizeof (errbuf)));
+    ERROR ("exec plugin: setuid (%i) failed: %s",
+	uid, sstrerror (errno, errbuf, sizeof (errbuf)));
     exit (-1);
   }
 
-- 
2.30.2