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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

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);
}