X-Git-Url: https://ruderich.org/simon/gitweb/?p=ptyas%2Fptyas.git;a=blobdiff_plain;f=ptyas.c;h=25f49aa2fc81ebb3d935ec87403857d8606a25a2;hp=70b1bf3918fb45c909bb4ee745fc6950d813dcc4;hb=09096d9ba0eb9bc938b7bd050a89abd949bf7257;hpb=66160644175cf5be5f0400594d1ce65b4de0fd0c
diff --git a/ptyas.c b/ptyas.c
index 70b1bf3..25f49aa 100644
--- a/ptyas.c
+++ b/ptyas.c
@@ -2,20 +2,20 @@
* 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) 2016-2019 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
+ * it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
+ * GNU Affero General Public License for more details.
*
- * You should have received a copy of the GNU General Public License
- * along with this program. If not, see .
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see .
*/
#define _GNU_SOURCE
@@ -82,9 +82,11 @@ static void open_pty_or_die(int *pty_master, int *pty_slave, uid_t uid) {
if (*pty_slave == -1) {
die("open slave tty");
}
- /* The user must be able to write to the new TTY. Normally grantpt() would
+ /*
+ * The user must be able to write to the new TTY. Normally grantpt() would
* do this for us, but we don't trust the user and thus don't want to pass
- * the pty_master to a process running under that uid. */
+ * the pty_master to a process running under that uid.
+ */
if (chown(slave_path, uid, (gid_t)-1) != 0) {
die("chown slave tty");
}
@@ -119,7 +121,7 @@ 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 +219,15 @@ 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;
@@ -267,10 +270,12 @@ static void proxy_input_between_ttys(int pty_master, int ctty, volatile pid_t *p
static volatile pid_t pid_to_wait_for;
static int pid_to_wait_for_status;
-static void sigchld_handler() {
+static void sigchld_handler(int signal) {
int status;
pid_t pid;
+ (void)signal;
+
while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
if (pid == pid_to_wait_for) {
/* Mark that our child has died and we should exit as well. */
@@ -281,6 +286,28 @@ static void sigchld_handler() {
}
}
+/*
+ * SIGWINCH handler to handle resizes of the outer terminal.
+ *
+ * Errors are ignored without message because printing in signal handlers is
+ * problematic (no FILE * usable due to locks) and there's not much we can do
+ * at this point.
+ */
+static int sigwinch_ctty = -1;
+static int sigwinch_slave = -1;
+
+static void sigwinch_handler(int signal) {
+ (void)signal;
+
+ struct winsize size;
+ if (ioctl(sigwinch_ctty, TIOCGWINSZ, &size) == -1) {
+ return;
+ }
+ if (ioctl(sigwinch_slave, TIOCSWINSZ, &size) == -1) {
+ return;
+ }
+}
+
int main(int argc, char **argv) {
char *exec_argv_shell[] = { NULL, NULL }; /* filled below */
@@ -360,6 +387,11 @@ 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);
@@ -374,6 +406,14 @@ 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];
@@ -404,14 +444,26 @@ int main(int argc, char **argv) {
}
quit_with_matching_code(status);
}
- close_or_die(pty_slave);
+ /* Don't close pty_slave here as it's used in sigwinch_handler(). */
+
+ sigwinch_ctty = ctty;
+ sigwinch_slave = pty_slave;
+
+ struct sigaction action_sigwinch = {
+ .sa_handler = sigwinch_handler,
+ };
+ sigemptyset(&action_sigwinch.sa_mask);
+ if (sigaction(SIGWINCH, &action_sigwinch, NULL) != 0) {
+ die("sigaction SIGWINCH");
+ }
pid_to_wait_for = pid;
- struct sigaction action = {
+ struct sigaction action_sigchld = {
.sa_handler = sigchld_handler,
};
- if (sigaction(SIGCHLD, &action, NULL) != 0) {
- die("sigaction");
+ sigemptyset(&action_sigchld.sa_mask);
+ if (sigaction(SIGCHLD, &action_sigchld, NULL) != 0) {
+ die("sigaction SIGCHLD");
}
if (sigprocmask(SIG_SETMASK, &sigset_old, NULL) != 0) {
@@ -442,8 +494,10 @@ 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");
}