drop privileges when running as group utmp

[wall-notify/wall-notify.git] / src / wall-notify.c

diff --git a/src/wall-notify.c b/src/wall-notify.c
index 7fb3b33cbc0bdaaf2e7436abf77bd7ca4b8d4fa1..292b71a1d9d026208db979be56cc5c03bdffb4d0 100644 (file)
--- a/src/wall-notify.c
+++ b/src/wall-notify.c
@@ -42,6 +42,10 @@
 #ifdef USE_UTMPX
 # include <utmpx.h>
 #endif
+#ifndef DONT_USE_X11
+# include <pthread.h>
+# include <X11/Xlib.h>
+#endif
 
 
 static void sig_handler(int signal) {
@@ -199,6 +203,44 @@ static int wait_for_write(int fd, int timeout) {
     return 1;
 }
 
+#ifdef USE_UTMPX
+static void drop_privileges(void) {
+    uid_t uid, ruid, euid, suid;
+    gid_t gid, rgid, egid, sgid;
+
+    uid = getuid();
+    gid = getgid();
+
+    /* Drop all privileges. */
+    if (setresuid(uid, uid, uid) != 0) {
+        perror("setresuid");
+        exit(EXIT_FAILURE);
+    }
+    if (setresgid(gid, gid, gid) != 0) {
+        perror("setresgid");
+        exit(EXIT_FAILURE);
+    }
+
+    /* Verify all privileges were dropped. */
+    if (getresuid(&ruid, &euid, &suid) != 0) {
+        perror("getresuid");
+        exit(EXIT_FAILURE);
+    }
+    if (getresgid(&rgid, &egid, &sgid) != 0) {
+        perror("getresgid");
+        exit(EXIT_FAILURE);
+    }
+    if (uid == ruid && uid == euid && uid == suid
+            && gid == rgid && gid == egid && gid == sgid) {
+        /* Everything fine. */
+        return;
+    }
+
+    fprintf(stderr, "failed to drop privileges, aborting\n");
+    exit(EXIT_FAILURE);
+}
+#endif
+
 static void pass_buffer_to_program(const char *buffer, size_t length, char **argv) {
     int fds[2];
     FILE *fh;
@@ -225,6 +267,10 @@ static void pass_buffer_to_program(const char *buffer, size_t length, char **arg
     } else if (pid == 0) {
         /* child */
 
+#ifdef USE_UTMPX
+        drop_privileges();
+#endif
+
         close(fds[1]); /* write side */
 
         /* Pass read side as stdin to the program. */
@@ -290,6 +336,27 @@ static void handle_wall(int fd, char **argv) {
         pass_buffer_to_program(buffer, (size_t)r, argv);
     }
 }
+#ifndef DONT_USE_X11
+static void *x11_event_loop_thread(void *unused) {
+    Display *display;
+    XEvent event;
+
+    (void)unused;
+
+    pthread_detach(pthread_self());
+
+    display = XOpenDisplay(NULL);
+    if (!display) {
+        fprintf(stderr, "failed to connect to X server\n");
+        exit(EXIT_FAILURE);
+    }
+
+    /* Do nothing. We just want to die if the X11 session is closed. */
+    while (1) {
+        XNextEvent(display, &event);
+    }
+}
+#endif
 
 static void usage(const char *argv0) {
     fprintf(stderr, "usage: %s <cmd args..>\n", argv0);
@@ -333,6 +400,19 @@ int main(int argc, char **argv) {
         exit(EXIT_FAILURE);
     }
 
+#ifndef DONT_USE_X11
+    /* Start a thread which connects to X11. This way we die if the user logs
+     * out of its X11 session. */
+    {
+        pthread_t tid;
+
+        if (pthread_create(&tid, NULL, x11_event_loop_thread, NULL) != 0) {
+            perror("pthread_create");
+            exit(EXIT_FAILURE);
+        }
+    }
+#endif
+
     /* Cleanup on signals. Necessary before login(). */
     setup_signals();