X-Git-Url: https://ruderich.org/simon/gitweb/?p=ptyas%2Fptyas.git;a=blobdiff_plain;f=ptyas.c;h=9ffe998a7f51c25deedfae106ddb166c68b676ba;hp=70b1bf3918fb45c909bb4ee745fc6950d813dcc4;hb=db05939cd070914c210343a5b2ae609d8fdc3f93;hpb=66160644175cf5be5f0400594d1ce65b4de0fd0c

diff --git a/ptyas.c b/ptyas.c
index 70b1bf3..9ffe998 100644
--- 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
@@ -119,7 +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. */
@@ -217,14 +217,13 @@ 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.) */
+         * 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;
@@ -360,6 +359,9 @@ 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);
@@ -374,6 +376,12 @@ 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];
@@ -442,7 +450,7 @@ int main(int argc, char **argv) {
         die("tcsetattr restore");
     }
 
-    /* Wait until we got the status code from our child. poll() might also
+    /* 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");