Commit a4a3e061 authored Mar 04, 2017 by Dmitry Vyukov Committed by Greg Kroah-Hartman Mar 17, 2017

tty: fix data race in tty_ldisc_ref_wait()



tty_ldisc_ref_wait() checks tty->ldisc under tty->ldisc_sem.
But if ldisc==NULL it releases them sem and reloads
tty->ldisc without holding the sem. This is wrong and
can lead to returning non-NULL ldisc without protection.

Don't reload tty->ldisc second time.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: syzkaller@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 5362544b

drivers/tty/tty_ldisc.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -271,10 +271,13 @@ const struct file_operations tty_ldiscs_proc_fops = {

		struct tty_ldisc tty_ldisc_ref_wait(struct tty_struct tty)
		{
		struct tty_ldisc *ld;

		ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
		if (!tty->ldisc)
		ld = tty->ldisc;
		if (!ld)
		ldsem_up_read(&tty->ldisc_sem);
		return tty->ldisc;
		return ld;
		}
		EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);

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