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/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
This file is part of systemd.
Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
/*
* PTY
* A PTY object represents a single PTY connection between a master and a
* child. The child process is fork()ed so the caller controls what program
* will be run.
*
* Programs like /bin/login tend to perform a vhangup() on their TTY
* before running the login procedure. This also causes the pty master
* to get a EPOLLHUP event as long as no client has the TTY opened.
* This means, we cannot use the TTY connection as reliable way to track
* the client. Instead, we _must_ rely on the PID of the client to track
* them.
* However, this has the side effect that if the client forks and the
* parent exits, we loose them and restart the client. But this seems to
* be the expected behavior so we implement it here.
*
* Unfortunately, epoll always polls for EPOLLHUP so as long as the
* vhangup() is ongoing, we will _always_ get EPOLLHUP and cannot sleep.
* This gets worse if the client closes the TTY but doesn't exit.
* Therefore, the fd must be edge-triggered in the epoll-set so we
* only get the events once they change.
*/
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <linux/ioctl.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/eventfd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <sys/wait.h>
#include <termios.h>
#include <unistd.h>
#include "barrier.h"
#include "macro.h"
#include "pty.h"
#include "ring.h"
#include "util.h"
#define PTY_BUFSIZE 4096
enum {
PTY_ROLE_UNKNOWN,
PTY_ROLE_PARENT,
PTY_ROLE_CHILD,
};
struct Pty {
unsigned long ref;
Barrier barrier;
int fd;
pid_t child;
sd_event_source *fd_source;
sd_event_source *child_source;
char in_buf[PTY_BUFSIZE];
Ring out_buf;
pty_event_t event_fn;
void *event_fn_userdata;
bool needs_requeue : 1;
unsigned int role : 2;
};
int pty_new(Pty **out) {
_pty_unref_ Pty *pty = NULL;
int r;
assert_return(out, -EINVAL);
pty = new0(Pty, 1);
if (!pty)
return -ENOMEM;
pty->ref = 1;
pty->fd = -1;
pty->barrier = (Barrier) BARRIER_NULL;
pty->fd = posix_openpt(O_RDWR | O_NOCTTY | O_CLOEXEC | O_NONBLOCK);
if (pty->fd < 0)
return -errno;
/*
* The slave-node is initialized to uid/gid of the caller of
* posix_openpt(). Only if devpts is mounted with fixed uid/gid this is
* skipped. In that case, grantpt() can overwrite these, but then you
* have to be root to use chown() (or a pt_chown helper has to be
* present). In those cases grantpt() really does something,
* otherwise it's a no-op. We call grantpt() here to try supporting
* those cases, even though no-one uses that, I guess. If you need other
* access-rights, set them yourself after this call returns (no, this is
* not racy, it looks racy, but races regarding your own UID are never
* important as an attacker could ptrace you; and the slave-pty is also
* still locked).
*/
r = grantpt(pty->fd);
if (r < 0)
return -errno;
r = barrier_create(&pty->barrier);
if (r < 0)
return r;
*out = pty;
pty = NULL;
return 0;
}
Pty *pty_ref(Pty *pty) {
if (!pty || pty->ref < 1)
return NULL;
++pty->ref;
return pty;
}
Pty *pty_unref(Pty *pty) {
if (!pty || pty->ref < 1 || --pty->ref > 0)
return NULL;
pty_close(pty);
pty->child_source = sd_event_source_unref(pty->child_source);
barrier_destroy(&pty->barrier);
ring_clear(&pty->out_buf);
free(pty);
return NULL;
}
Barrier *pty_get_barrier(Pty *pty) {
assert(pty);
return &pty->barrier;
}
bool pty_is_unknown(Pty *pty) {
return pty && pty->role == PTY_ROLE_UNKNOWN;
}
bool pty_is_parent(Pty *pty) {
return pty && pty->role == PTY_ROLE_PARENT;
}
bool pty_is_child(Pty *pty) {
return pty && pty->role == PTY_ROLE_CHILD;
}
bool pty_has_child(Pty *pty) {
return pty_is_parent(pty) && pty->child > 0;
}
pid_t pty_get_child(Pty *pty) {
return pty_has_child(pty) ? pty->child : -ECHILD;
}
bool pty_is_open(Pty *pty) {
return pty && pty->fd >= 0;
}
int pty_get_fd(Pty *pty) {
assert_return(pty, -EINVAL);
return pty_is_open(pty) ? pty->fd : -EPIPE;
}
int pty_make_child(Pty *pty) {
char slave_name[1024];
int r, fd;
assert_return(pty, -EINVAL);
assert_return(pty_is_unknown(pty), -EALREADY);
r = ptsname_r(pty->fd, slave_name, sizeof(slave_name));
if (r < 0)
return -errno;
fd = open(slave_name, O_RDWR | O_CLOEXEC | O_NOCTTY);
if (fd < 0)
return -errno;
safe_close(pty->fd);
pty->fd = fd;
pty->child = getpid();
pty->role = PTY_ROLE_CHILD;
barrier_set_role(&pty->barrier, BARRIER_CHILD);
return 0;
}
int pty_make_parent(Pty *pty, pid_t child) {
assert_return(pty, -EINVAL);
assert_return(pty_is_unknown(pty), -EALREADY);
pty->child = child;
pty->role = PTY_ROLE_PARENT;
return 0;
}
int pty_unlock(Pty *pty) {
assert_return(pty, -EINVAL);
assert_return(pty_is_unknown(pty) || pty_is_parent(pty), -EINVAL);
assert_return(pty_is_open(pty), -ENODEV);
return unlockpt(pty->fd) < 0 ? -errno : 0;
}
int pty_setup_child(Pty *pty) {
struct termios attr;
pid_t pid;
int r;
assert_return(pty, -EINVAL);
assert_return(pty_is_child(pty), -EINVAL);
assert_return(pty_is_open(pty), -EALREADY);
r = sigprocmask_many(SIG_SETMASK, -1);
if (r < 0)
return r;
r = reset_all_signal_handlers();
if (r < 0)
return r;
pid = setsid();
if (pid < 0 && errno != EPERM)
return -errno;
r = ioctl(pty->fd, TIOCSCTTY, 0);
if (r < 0)
return -errno;
r = tcgetattr(pty->fd, &attr);
if (r < 0)
return -errno;
/* erase character should be normal backspace, PLEASEEE! */
attr.c_cc[VERASE] = 010;
/* always set UTF8 flag */
attr.c_iflag |= IUTF8;
r = tcsetattr(pty->fd, TCSANOW, &attr);
if (r < 0)
return -errno;
if (dup2(pty->fd, STDIN_FILENO) != STDIN_FILENO ||
dup2(pty->fd, STDOUT_FILENO) != STDOUT_FILENO ||
dup2(pty->fd, STDERR_FILENO) != STDERR_FILENO)
return -errno;
/* only close FD if it's not a std-fd */
pty->fd = (pty->fd > 2) ? safe_close(pty->fd) : -1;
return 0;
}
void pty_close(Pty *pty) {
if (!pty_is_open(pty))
return;
pty->fd_source = sd_event_source_unref(pty->fd_source);
pty->fd = safe_close(pty->fd);
}
/*
* Drain input-queue and dispatch data via the event-handler. Returns <0 on
* error, 0 if queue is empty and 1 if we couldn't empty the input queue fast
* enough and there's still data left.
*/
static int pty_dispatch_read(Pty *pty) {
unsigned int i;
ssize_t len;
int r;
/*
* We're edge-triggered, means we need to read the whole queue. This,
* however, might cause us to stall if the writer is faster than we
* are. Therefore, try reading as much as 8 times (32KiB) and only
* bail out then.
*/
for (i = 0; i < 8; ++i) {
len = read(pty->fd, pty->in_buf, sizeof(pty->in_buf) - 1);
if (len < 0) {
if (errno == EINTR)
continue;
return (errno == EAGAIN) ? 0 : -errno;
} else if (len == 0) {
continue;
}
/* set terminating zero for debugging safety */
pty->in_buf[len] = 0;
r = pty->event_fn(pty, pty->event_fn_userdata, PTY_DATA, pty->in_buf, len);
if (r < 0)
return r;
}
/* still data left, make sure we're queued again */
pty->needs_requeue = true;
return 1;
}
/*
* Drain output-queue by writing data to the pty. Returns <0 on error, 0 if the
* output queue is empty now and 1 if we couldn't empty the output queue fast
* enough and there's still data left.
*/
static int pty_dispatch_write(Pty *pty) {
struct iovec vec[2];
unsigned int i;
ssize_t len;
size_t num;
/*
* Same as pty_dispatch_read(), we're edge-triggered so we need to call
* write() until either all data is written or it returns EAGAIN. We
* call it twice and if it still writes successfully, we reschedule.
*/
for (i = 0; i < 2; ++i) {
num = ring_peek(&pty->out_buf, vec);
if (num < 1)
return 0;
len = writev(pty->fd, vec, (int)num);
if (len < 0) {
if (errno == EINTR)
continue;
return (errno == EAGAIN) ? 1 : -errno;
} else if (len == 0) {
continue;
}
ring_pull(&pty->out_buf, (size_t)len);
}
/* still data left, make sure we're queued again */
if (ring_get_size(&pty->out_buf) > 0) {
pty->needs_requeue = true;
return 1;
}
return 0;
}
static int pty_fd_fn(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
Pty *pty = userdata;
int r_hup = 0, r_write = 0, r_read = 0, r;
/*
* Whenever we encounter I/O errors, we have to make sure to drain the
* input queue first, before we handle any HUP. A child might send us
* a message and immediately close the queue. We must not handle the
* HUP first or we loose data.
* Therefore, if we read a message successfully, we always return
* success and wait for the next event-loop iteration. Furthermore,
* whenever there is a write-error, we must try reading from the input
* queue even if EPOLLIN is not set. The input might have arrived in
* between epoll_wait() and write(). Therefore, write-errors are only
* ever handled if the input-queue is empty. In all other cases they
* are ignored until either reading fails or the input queue is empty.
*/
if (revents & (EPOLLHUP | EPOLLERR))
r_hup = -EPIPE;
if (revents & EPOLLOUT)
r_write = pty_dispatch_write(pty);
/* Awesome! Kernel signals HUP without IN but queues are not empty.. */
if ((revents & EPOLLIN) || r_hup < 0 || r_write < 0) {
r_read = pty_dispatch_read(pty);
if (r_read > 0)
return 0; /* still data left to fetch next round */
}
if (r_hup < 0 || r_write < 0 || r_read < 0) {
/* PTY closed and input-queue drained */
pty_close(pty);
r = pty->event_fn(pty, pty->event_fn_userdata, PTY_HUP, NULL, 0);
if (r < 0)
return r;
}
return 0;
}
static int pty_fd_prepare_fn(sd_event_source *source, void *userdata) {
Pty *pty = userdata;
int r;
if (pty->needs_requeue) {
/*
* We're edge-triggered. In case we couldn't handle all events
* or in case new write-data is queued, we set needs_requeue.
* Before going asleep, we set the io-events *again*. sd-event
* notices that we're edge-triggered and forwards the call to
* the kernel even if the events didn't change. The kernel will
* check the events and re-queue us on the ready queue in case
* an event is pending.
*/
r = sd_event_source_set_io_events(source, EPOLLHUP | EPOLLERR | EPOLLIN | EPOLLOUT | EPOLLET);
if (r >= 0)
pty->needs_requeue = false;
}
return 0;
}
static int pty_child_fn(sd_event_source *source, const siginfo_t *si, void *userdata) {
Pty *pty = userdata;
int r;
pty->child = 0;
r = pty->event_fn(pty, pty->event_fn_userdata, PTY_CHILD, si, sizeof(*si));
if (r < 0)
return r;
return 0;
}
int pty_attach_event(Pty *pty, sd_event *event, pty_event_t event_fn, void *event_fn_userdata) {
int r;
assert_return(pty, -EINVAL);
assert_return(event, -EINVAL);
assert_return(event_fn, -EINVAL);
assert_return(pty_is_parent(pty), -EINVAL);
pty_detach_event(pty);
if (pty_is_open(pty)) {
r = sd_event_add_io(event,
&pty->fd_source,
pty->fd,
EPOLLHUP | EPOLLERR | EPOLLIN | EPOLLOUT | EPOLLET,
pty_fd_fn,
pty);
if (r < 0)
goto error;
r = sd_event_source_set_prepare(pty->fd_source, pty_fd_prepare_fn);
if (r < 0)
goto error;
}
if (pty_has_child(pty)) {
r = sd_event_add_child(event,
&pty->child_source,
pty->child,
WEXITED,
pty_child_fn,
pty);
if (r < 0)
goto error;
}
pty->event_fn = event_fn;
pty->event_fn_userdata = event_fn_userdata;
return 0;
error:
pty_detach_event(pty);
return r;
}
void pty_detach_event(Pty *pty) {
if (!pty)
return;
pty->child_source = sd_event_source_unref(pty->child_source);
pty->fd_source = sd_event_source_unref(pty->fd_source);
pty->event_fn = NULL;
pty->event_fn_userdata = NULL;
}
int pty_write(Pty *pty, const void *buf, size_t size) {
bool was_empty;
int r;
assert_return(pty, -EINVAL);
assert_return(pty_is_open(pty), -ENODEV);
assert_return(pty_is_parent(pty), -ENODEV);
if (size < 1)
return 0;
/*
* Push @buf[0..@size] into the output ring-buffer. In case the
* ring-buffer wasn't empty beforehand, we're already waiting for
* EPOLLOUT and we're done. If it was empty, we have to re-queue the
* FD for EPOLLOUT as we're edge-triggered and wouldn't get any new
* EPOLLOUT event.
*/
was_empty = ring_get_size(&pty->out_buf) < 1;
r = ring_push(&pty->out_buf, buf, size);
if (r < 0)
return r;
if (was_empty)
pty->needs_requeue = true;
return 0;
}
int pty_signal(Pty *pty, int sig) {
assert_return(pty, -EINVAL);
assert_return(pty_is_open(pty), -ENODEV);
assert_return(pty_is_parent(pty), -ENODEV);
return ioctl(pty->fd, TIOCSIG, sig) < 0 ? -errno : 0;
}
int pty_resize(Pty *pty, unsigned short term_width, unsigned short term_height) {
struct winsize ws;
assert_return(pty, -EINVAL);
assert_return(pty_is_open(pty), -ENODEV);
assert_return(pty_is_parent(pty), -ENODEV);
zero(ws);
ws.ws_col = term_width;
ws.ws_row = term_height;
/*
* This will send SIGWINCH to the pty slave foreground process group.
* We will also get one, but we don't need it.
*/
return ioctl(pty->fd, TIOCSWINSZ, &ws) < 0 ? -errno : 0;
}
pid_t pty_fork(Pty **out, sd_event *event, pty_event_t event_fn, void *event_fn_userdata, unsigned short initial_term_width, unsigned short initial_term_height) {
_pty_unref_ Pty *pty = NULL;
int r;
pid_t pid;
assert_return(out, -EINVAL);
assert_return((event && event_fn) || (!event && !event_fn), -EINVAL);
r = pty_new(&pty);
if (r < 0)
return r;
r = pty_unlock(pty);
if (r < 0)
return r;
pid = fork();
if (pid < 0)
return -errno;
if (pid == 0) {
/* child */
r = pty_make_child(pty);
if (r < 0)
_exit(-r);
r = pty_setup_child(pty);
if (r < 0)
_exit(-r);
/* sync with parent */
if (!barrier_place_and_sync(&pty->barrier))
_exit(1);
/* fallthrough and return the child's PTY object */
} else {
/* parent */
r = pty_make_parent(pty, pid);
if (r < 0)
goto parent_error;
r = pty_resize(pty, initial_term_width, initial_term_height);
if (r < 0)
goto parent_error;
if (event) {
r = pty_attach_event(pty, event, event_fn, event_fn_userdata);
if (r < 0)
goto parent_error;
}
/* sync with child */
if (!barrier_place_and_sync(&pty->barrier)) {
r = -ECHILD;
goto parent_error;
}
/* fallthrough and return the parent's PTY object */
}
*out = pty;
pty = NULL;
return pid;
parent_error:
barrier_abort(&pty->barrier);
waitpid(pty->child, NULL, 0);
pty->child = 0;
return r;
}