linux/arch/um/drivers/chan_user.c
Anton Ivanov 9b1c0c0e25 um: tty: Fix handling of close in tty lines
Fix a logical error in tty reading. We get 0 and errno == EAGAIN
on the first attempt to read from a closed file descriptor.

Compared to that a true EAGAIN is EAGAIN and -1.

If we check errno for EAGAIN first, before checking the return
value we miss the fact that the descriptor is closed.

This bug is as old as the driver. It was not showing up with
the original POLL based IRQ controller, because it was
producing multiple events. Switching to EPOLL unmasked it.

Fixes: ff6a17989c ("Epoll based IRQ controller")
Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
2020-12-13 22:38:28 +01:00

302 lines
7.0 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2000 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
*/
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <termios.h>
#include <sys/ioctl.h>
#include "chan_user.h"
#include <os.h>
#include <um_malloc.h>
void generic_close(int fd, void *unused)
{
close(fd);
}
int generic_read(int fd, char *c_out, void *unused)
{
int n;
n = read(fd, c_out, sizeof(*c_out));
if (n > 0)
return n;
else if (n == 0)
return -EIO;
else if (errno == EAGAIN)
return 0;
return -errno;
}
/* XXX Trivial wrapper around write */
int generic_write(int fd, const char *buf, int n, void *unused)
{
int err;
err = write(fd, buf, n);
if (err > 0)
return err;
else if (errno == EAGAIN)
return 0;
else if (err == 0)
return -EIO;
return -errno;
}
int generic_window_size(int fd, void *unused, unsigned short *rows_out,
unsigned short *cols_out)
{
struct winsize size;
int ret;
if (ioctl(fd, TIOCGWINSZ, &size) < 0)
return -errno;
ret = ((*rows_out != size.ws_row) || (*cols_out != size.ws_col));
*rows_out = size.ws_row;
*cols_out = size.ws_col;
return ret;
}
void generic_free(void *data)
{
kfree(data);
}
int generic_console_write(int fd, const char *buf, int n)
{
sigset_t old, no_sigio;
struct termios save, new;
int err;
if (isatty(fd)) {
sigemptyset(&no_sigio);
sigaddset(&no_sigio, SIGIO);
if (sigprocmask(SIG_BLOCK, &no_sigio, &old))
goto error;
CATCH_EINTR(err = tcgetattr(fd, &save));
if (err)
goto error;
new = save;
/*
* The terminal becomes a bit less raw, to handle \n also as
* "Carriage Return", not only as "New Line". Otherwise, the new
* line won't start at the first column.
*/
new.c_oflag |= OPOST;
CATCH_EINTR(err = tcsetattr(fd, TCSAFLUSH, &new));
if (err)
goto error;
}
err = generic_write(fd, buf, n, NULL);
/*
* Restore raw mode, in any case; we *must* ignore any error apart
* EINTR, except for debug.
*/
if (isatty(fd)) {
CATCH_EINTR(tcsetattr(fd, TCSAFLUSH, &save));
sigprocmask(SIG_SETMASK, &old, NULL);
}
return err;
error:
return -errno;
}
/*
* UML SIGWINCH handling
*
* The point of this is to handle SIGWINCH on consoles which have host
* ttys and relay them inside UML to whatever might be running on the
* console and cares about the window size (since SIGWINCH notifies
* about terminal size changes).
*
* So, we have a separate thread for each host tty attached to a UML
* device (side-issue - I'm annoyed that one thread can't have
* multiple controlling ttys for the purpose of handling SIGWINCH, but
* I imagine there are other reasons that doesn't make any sense).
*
* SIGWINCH can't be received synchronously, so you have to set up to
* receive it as a signal. That being the case, if you are going to
* wait for it, it is convenient to sit in sigsuspend() and wait for
* the signal to bounce you out of it (see below for how we make sure
* to exit only on SIGWINCH).
*/
static void winch_handler(int sig)
{
}
struct winch_data {
int pty_fd;
int pipe_fd;
};
static int winch_thread(void *arg)
{
struct winch_data *data = arg;
sigset_t sigs;
int pty_fd, pipe_fd;
int count;
char c = 1;
pty_fd = data->pty_fd;
pipe_fd = data->pipe_fd;
count = write(pipe_fd, &c, sizeof(c));
if (count != sizeof(c))
printk(UM_KERN_ERR "winch_thread : failed to write "
"synchronization byte, err = %d\n", -count);
/*
* We are not using SIG_IGN on purpose, so don't fix it as I thought to
* do! If using SIG_IGN, the sigsuspend() call below would not stop on
* SIGWINCH.
*/
signal(SIGWINCH, winch_handler);
sigfillset(&sigs);
/* Block all signals possible. */
if (sigprocmask(SIG_SETMASK, &sigs, NULL) < 0) {
printk(UM_KERN_ERR "winch_thread : sigprocmask failed, "
"errno = %d\n", errno);
exit(1);
}
/* In sigsuspend(), block anything else than SIGWINCH. */
sigdelset(&sigs, SIGWINCH);
if (setsid() < 0) {
printk(UM_KERN_ERR "winch_thread : setsid failed, errno = %d\n",
errno);
exit(1);
}
if (ioctl(pty_fd, TIOCSCTTY, 0) < 0) {
printk(UM_KERN_ERR "winch_thread : TIOCSCTTY failed on "
"fd %d err = %d\n", pty_fd, errno);
exit(1);
}
if (tcsetpgrp(pty_fd, os_getpid()) < 0) {
printk(UM_KERN_ERR "winch_thread : tcsetpgrp failed on "
"fd %d err = %d\n", pty_fd, errno);
exit(1);
}
/*
* These are synchronization calls between various UML threads on the
* host - since they are not different kernel threads, we cannot use
* kernel semaphores. We don't use SysV semaphores because they are
* persistent.
*/
count = read(pipe_fd, &c, sizeof(c));
if (count != sizeof(c))
printk(UM_KERN_ERR "winch_thread : failed to read "
"synchronization byte, err = %d\n", errno);
while(1) {
/*
* This will be interrupted by SIGWINCH only, since
* other signals are blocked.
*/
sigsuspend(&sigs);
count = write(pipe_fd, &c, sizeof(c));
if (count != sizeof(c))
printk(UM_KERN_ERR "winch_thread : write failed, "
"err = %d\n", errno);
}
}
static int winch_tramp(int fd, struct tty_port *port, int *fd_out,
unsigned long *stack_out)
{
struct winch_data data;
int fds[2], n, err;
char c;
err = os_pipe(fds, 1, 1);
if (err < 0) {
printk(UM_KERN_ERR "winch_tramp : os_pipe failed, err = %d\n",
-err);
goto out;
}
data = ((struct winch_data) { .pty_fd = fd,
.pipe_fd = fds[1] } );
/*
* CLONE_FILES so this thread doesn't hold open files which are open
* now, but later closed in a different thread. This is a
* problem with /dev/net/tun, which if held open by this
* thread, prevents the TUN/TAP device from being reused.
*/
err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
if (err < 0) {
printk(UM_KERN_ERR "fork of winch_thread failed - errno = %d\n",
-err);
goto out_close;
}
*fd_out = fds[0];
n = read(fds[0], &c, sizeof(c));
if (n != sizeof(c)) {
printk(UM_KERN_ERR "winch_tramp : failed to read "
"synchronization byte\n");
printk(UM_KERN_ERR "read failed, err = %d\n", errno);
printk(UM_KERN_ERR "fd %d will not support SIGWINCH\n", fd);
err = -EINVAL;
goto out_close;
}
if (os_set_fd_block(*fd_out, 0)) {
printk(UM_KERN_ERR "winch_tramp: failed to set thread_fd "
"non-blocking.\n");
goto out_close;
}
return err;
out_close:
close(fds[1]);
close(fds[0]);
out:
return err;
}
void register_winch(int fd, struct tty_port *port)
{
unsigned long stack;
int pid, thread, count, thread_fd = -1;
char c = 1;
if (!isatty(fd))
return;
pid = tcgetpgrp(fd);
if (is_skas_winch(pid, fd, port)) {
register_winch_irq(-1, fd, -1, port, 0);
return;
}
if (pid == -1) {
thread = winch_tramp(fd, port, &thread_fd, &stack);
if (thread < 0)
return;
register_winch_irq(thread_fd, fd, thread, port, stack);
count = write(thread_fd, &c, sizeof(c));
if (count != sizeof(c))
printk(UM_KERN_ERR "register_winch : failed to write "
"synchronization byte, err = %d\n", errno);
}
}