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Fix OpenSSH pty regression on close

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OpenSSH expects the (non-blocking) read() of pty master to return
EAGAIN only if it has received all of the slave-side output after
it has received SIGCHLD. This used to work on pre-3.12 kernels.

This fix effectively forces non-blocking read() and poll() to
block for parallel i/o to complete for all ttys. It also unwinds
these changes:

1) f8747d4a46
   tty: Fix pty master read() after slave closes

2) 52bce7f8d4
   pty, n_tty: Simplify input processing on final close

3) 1a48632ffe
   pty: Fix input race when closing

Inspired by analysis and patch from Marc Aurele La France <tsi@tuyoix.net>

Reported-by: Volth <openssh@volth.com>
Reported-by: Marc Aurele La France <tsi@tuyoix.net>
BugLink: https://bugzilla.mindrot.org/show_bug.cgi?id=52
BugLink: https://bugzilla.mindrot.org/show_bug.cgi?id=2492
Signed-off-by: Brian Bloniarz <brian.bloniarz@gmail.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Brian Bloniarz
2016-03-06 13:16:30 -08:00
committed by Greg Kroah-Hartman
parent d11df61853
commit 0f40fbbcc3
6 changed files with 44 additions and 75 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/tty/n_hdlc.c
View File

@@ -599,7 +599,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
add_wait_queue(&tty->read_wait, &wait);
for (;;) {
if (test_bit(TTY_OTHER_DONE, &tty->flags)) {
if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
ret = -EIO;
break;
}
@@ -827,7 +827,7 @@ static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
/* set bits for operations that won't block */
if (n_hdlc->rx_buf_list.head)
mask |= POLLIN | POLLRDNORM; /* readable */
if (test_bit(TTY_OTHER_DONE, &tty->flags))
if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
mask |= POLLHUP;
if (tty_hung_up_p(filp))
mask |= POLLHUP;

72
drivers/tty/n_tty.c
View File

@@ -1917,18 +1917,6 @@ static inline int input_available_p(struct tty_struct *tty, int poll)
return ldata->commit_head - ldata->read_tail >= amt;
}
static inline int check_other_done(struct tty_struct *tty)
{
int done = test_bit(TTY_OTHER_DONE, &tty->flags);
if (done) {
/* paired with cmpxchg() in check_other_closed(); ensures
* read buffer head index is not stale
*/
smp_mb__after_atomic();
}
return done;
}
/**
* copy_from_read_buf - copy read data directly
* @tty: terminal device
@@ -2124,7 +2112,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
struct n_tty_data *ldata = tty->disc_data;
unsigned char __user *b = buf;
DEFINE_WAIT_FUNC(wait, woken_wake_function);
int c, done;
int c;
int minimum, time;
ssize_t retval = 0;
long timeout;
@@ -2183,32 +2171,35 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
break;
}
done = check_other_done(tty);
if (!input_available_p(tty, 0)) {
if (done) {
retval = -EIO;
break;
}
if (tty_hung_up_p(file))
break;
if (!timeout)
break;
if (file->f_flags & O_NONBLOCK) {
retval = -EAGAIN;
break;
}
if (signal_pending(current)) {
retval = -ERESTARTSYS;
break;
}
up_read(&tty->termios_rwsem);
timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
timeout);
tty_buffer_flush_work(tty->port);
down_read(&tty->termios_rwsem);
continue;
if (!input_available_p(tty, 0)) {
if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
retval = -EIO;
break;
}
if (tty_hung_up_p(file))
break;
if (!timeout)
break;
if (file->f_flags & O_NONBLOCK) {
retval = -EAGAIN;
break;
}
if (signal_pending(current)) {
retval = -ERESTARTSYS;
break;
}
up_read(&tty->termios_rwsem);
timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
timeout);
down_read(&tty->termios_rwsem);
continue;
}
}
if (ldata->icanon && !L_EXTPROC(tty)) {
@@ -2386,12 +2377,17 @@ static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file,
poll_wait(file, &tty->read_wait, wait);
poll_wait(file, &tty->write_wait, wait);
if (check_other_done(tty))
mask |= POLLHUP;
if (input_available_p(tty, 1))
mask |= POLLIN | POLLRDNORM;
else {
tty_buffer_flush_work(tty->port);
if (input_available_p(tty, 1))
mask |= POLLIN | POLLRDNORM;
}
if (tty->packet && tty->link->ctrl_status)
mask |= POLLPRI | POLLIN | POLLRDNORM;
if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
mask |= POLLHUP;
if (tty_hung_up_p(file))
mask |= POLLHUP;
if (tty->ops->write && !tty_is_writelocked(tty) &&

4
drivers/tty/pty.c
View File

@@ -59,7 +59,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
if (!tty->link)
return;
set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
tty_flip_buffer_push(tty->link->port);
wake_up_interruptible(&tty->link->read_wait);
wake_up_interruptible(&tty->link->write_wait);
if (tty->driver->subtype == PTY_TYPE_MASTER) {
set_bit(TTY_OTHER_CLOSED, &tty->flags);
@@ -247,9 +247,7 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
goto out;
clear_bit(TTY_IO_ERROR, &tty->flags);
/* TTY_OTHER_CLOSED must be cleared before TTY_OTHER_DONE */
clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
clear_bit(TTY_OTHER_DONE, &tty->link->flags);
set_bit(TTY_THROTTLED, &tty->flags);
return 0;

34
drivers/tty/tty_buffer.c
View File

@@ -37,29 +37,6 @@
#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
/*
* If all tty flip buffers have been processed by flush_to_ldisc() or
* dropped by tty_buffer_flush(), check if the linked pty has been closed.
* If so, wake the reader/poll to process
*/
static inline void check_other_closed(struct tty_struct *tty)
{
unsigned long flags, old;
/* transition from TTY_OTHER_CLOSED => TTY_OTHER_DONE must be atomic */
for (flags = ACCESS_ONCE(tty->flags);
test_bit(TTY_OTHER_CLOSED, &flags);
) {
old = flags;
__set_bit(TTY_OTHER_DONE, &flags);
flags = cmpxchg(&tty->flags, old, flags);
if (old == flags) {
wake_up_interruptible(&tty->read_wait);
break;
}
}
}
/**
* tty_buffer_lock_exclusive - gain exclusive access to buffer
* tty_buffer_unlock_exclusive - release exclusive access
@@ -254,8 +231,6 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
if (ld && ld->ops->flush_buffer)
ld->ops->flush_buffer(tty);
check_other_closed(tty);
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
}
@@ -522,10 +497,8 @@ static void flush_to_ldisc(struct work_struct *work)
*/
count = smp_load_acquire(&head->commit) - head->read;
if (!count) {
if (next == NULL) {
check_other_closed(tty);
if (next == NULL)
break;
}
buf->head = next;
tty_buffer_free(port, head);
continue;
@@ -614,3 +587,8 @@ bool tty_buffer_cancel_work(struct tty_port *port)
{
return cancel_work_sync(&port->buf.work);
}
void tty_buffer_flush_work(struct tty_port *port)
{
flush_work(&port->buf.work);
}