Make multi-line comments consistent

[ptyas/ptyas.git] / ptyas.c

diff --git a/ptyas.c b/ptyas.c
index 1deda82a2e48cf265a73f5b86789bb98395fa2c9..e6ecd558405be523fe971a2f747bac905c1d00a9 100644 (file)
--- a/ptyas.c
+++ b/ptyas.c
@@ -2,7 +2,7 @@
  * Run the login shell or command as the given user in a new pty to prevent
  * terminal injection attacks.
  *
- * Copyright (C) 2016  Simon Ruderich
+ * Copyright (C) 2016-2017  Simon Ruderich
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -39,6 +39,12 @@
 #include <termios.h>
 #include <unistd.h>
 
+/* Default PATH for new process.*/
+#ifndef PTYAS_DEFAULT_PATH
+/* Default user PATH from Debian's /etc/profile, change as needed. */
+# define PTYAS_DEFAULT_PATH "/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games"
+#endif
+
 
 static void die(const char *s) {
     perror(s);
@@ -113,7 +119,7 @@ static void drop_privileges_or_die(uid_t uid, gid_t gid) {
         die("setgroups");
     }
     if (getgroups(0, NULL) != 0) {
-        die_fmt("failed to drop all groups");
+        die_fmt("failed to drop all supplementary groups");
     }
 
     /* Dropping groups may require privileges, do that first. */
@@ -211,14 +217,15 @@ static void proxy_input_between_ttys(int pty_master, int ctty, volatile pid_t *p
         if (ppoll(fds, nfds, NULL /* no timeout */, &sigset_old) == -1) {
             if (errno == EAGAIN || errno == EINTR) {
                 continue;
-            } else {
-                perror("poll");
             }
+            perror("poll");
             break;
         }
 
-        /* Handle errors first. (Data available before the error occurred
-         * might be skipped, but shouldn't matter here.) */
+        /*
+         * Handle errors first. (Data available before the error occurred
+         * might be dropped, but shouldn't matter here.)
+         */
         if (fds[0].revents & (POLLERR | POLLNVAL)) {
             fprintf(stderr, "poll: error on master: %d\n", fds[0].revents);
             break;
@@ -354,6 +361,11 @@ int main(int argc, char **argv) {
         if (pid == -1) {
             die("fork child");
         } else if (pid == 0) {
+            /*
+             * Drop the privileges just now so that the other user doesn't get
+             * access to the master TTY or the session leader (which might
+             * have additional privileges).
+             */
             drop_privileges_or_die(uid, gid);
 
             dup2_or_die(pty_slave, STDIN_FILENO);
@@ -368,6 +380,14 @@ int main(int argc, char **argv) {
             }
             const char *home = passwd->pw_dir;
 
+            /*
+             * Ignore errors here as we don't want to die on non-existent home
+             * directories to allow running as any user (think "/nonexistent"
+             * as home) and an error message will be annoying to ignore when
+             * running this command in scripts.
+             */
+            chdir(home);
+
             char envp_user[strlen("USER=") + strlen(user) + 1];
             char envp_home[strlen("HOME=") + strlen(home) + 1];
             char envp_term[strlen("TERM=") + strlen(term) + 1];
@@ -376,7 +396,7 @@ int main(int argc, char **argv) {
             snprintf_or_assert(envp_term, sizeof(envp_term), "TERM=%s", term);
 
             char *exec_envp[] = {
-                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
+                "PATH=" PTYAS_DEFAULT_PATH,
                 envp_user,
                 envp_home,
                 term_orig ? envp_term : NULL,
@@ -436,8 +456,10 @@ int main(int argc, char **argv) {
         die("tcsetattr restore");
     }
 
-    /* Wait until we got the status code from our child. poll() might also
-     * exit after POLLHUP while we haven't collected the child yet. */
+    /*
+     * Wait until we got the status code from our child. poll() might already
+     * exit after POLLHUP while we haven't collected the child yet.
+     */
     if (sigprocmask(SIG_BLOCK, &sigset, &sigset_old) != 0) {
         die("sigprocmask block sigchld loop");
     }