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tty: Retry failed reopen if tty teardown in-progress

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A small window exists where a tty reopen will observe the tty
just prior to imminent teardown (tty->count == 0); in this case, open()
returns EIO to userspace.

Instead, retry the open after checking for signals and yielding;
this interruptible retry loop allows teardown to commence and initialize
a new tty on retry. Never retry the BSD master pty reopen; there is no
guarantee the pty pair teardown is imminent since the slave file
descriptors may remain open indefinitely.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Cc: stable <stable@vger.kernel.org> # 4.4
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2016-01-09 21:13:45 -08:00 committed by Greg Kroah-Hartman
parent 0bfd464d3f
commit 7f22f6c935
1 changed files with 8 additions and 4 deletions
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12
drivers/tty/tty_io.c
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@ -1463,13 +1463,13 @@ static int tty_reopen(struct tty_struct *tty)
{ {
struct tty_driver *driver = tty->driver; struct tty_driver *driver = tty->driver;
if (!tty->count)
return -EIO;
if (driver->type == TTY_DRIVER_TYPE_PTY && if (driver->type == TTY_DRIVER_TYPE_PTY &&
driver->subtype == PTY_TYPE_MASTER) driver->subtype == PTY_TYPE_MASTER)
return -EIO; return -EIO;
if (!tty->count)
return -EAGAIN;
if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
return -EBUSY; return -EBUSY;
@ -2088,7 +2088,11 @@ static int tty_open(struct inode *inode, struct file *filp)
if (IS_ERR(tty)) { if (IS_ERR(tty)) {
retval = PTR_ERR(tty); retval = PTR_ERR(tty);
goto err_file; if (retval != -EAGAIN || signal_pending(current))
goto err_file;
tty_free_file(filp);
schedule();
goto retry_open;
} }
tty_add_file(tty, filp); tty_add_file(tty, filp);