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authorDmitry Vyukov <dvyukov@google.com>2017-03-04 13:46:12 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-03-17 14:07:10 +0900
commita4a3e061149f09c075f108b6f1cf04d9739a6bc2 (patch)
tree1539f1e567023aeda89d8ea8af68d885d6b8f7dd /drivers/tty
parent5362544bebe85071188dd9e479b5a5040841c895 (diff)
downloadlinux-a4a3e061149f09c075f108b6f1cf04d9739a6bc2.tar.bz2
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>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/tty_ldisc.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index c3956ca022e4..b0500a0a87b8 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -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);