[3.19.y-ckt stable] Patch "net: irda: Fix use-after-free in irtty_open()" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    net: irda: Fix use-after-free in irtty_open()

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt18.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 49fa19788dfe8f3163f03b3796b9b4dc18d64459 Mon Sep 17 00:00:00 2001
From: Peter Hurley <peter at hurleysoftware.com>
Date: Sat, 9 Jan 2016 17:48:45 -0800
Subject: net: irda: Fix use-after-free in irtty_open()

commit 401879c57f01cbf2da204ad2e8db910525c6dbea upstream.

The N_IRDA line discipline may access the previous line discipline's closed
and already-fre private data on open [1].

The tty->disc_data field _never_ refers to valid data on entry to the
line discipline's open() method. Rather, the ldisc is expected to
initialize that field for its own use for the lifetime of the instance
(ie. from open() to close() only).

[1]
    ==================================================================
    BUG: KASAN: use-after-free in irtty_open+0x422/0x550 at addr ffff8800331dd068
    Read of size 4 by task a.out/13960
    =============================================================================
    BUG kmalloc-512 (Tainted: G    B          ): kasan: bad access detected
    -----------------------------------------------------------------------------
    ...
    Call Trace:
     [<ffffffff815fa2ae>] __asan_report_load4_noabort+0x3e/0x40 mm/kasan/report.c:279
     [<ffffffff836938a2>] irtty_open+0x422/0x550 drivers/net/irda/irtty-sir.c:436
     [<ffffffff829f1b80>] tty_ldisc_open.isra.2+0x60/0xa0 drivers/tty/tty_ldisc.c:447
     [<ffffffff829f21c0>] tty_set_ldisc+0x1a0/0x940 drivers/tty/tty_ldisc.c:567
     [<     inline     >] tiocsetd drivers/tty/tty_io.c:2650
     [<ffffffff829da49e>] tty_ioctl+0xace/0x1fd0 drivers/tty/tty_io.c:2883
     [<     inline     >] vfs_ioctl fs/ioctl.c:43
     [<ffffffff816708ac>] do_vfs_ioctl+0x57c/0xe60 fs/ioctl.c:607
     [<     inline     >] SYSC_ioctl fs/ioctl.c:622
     [<ffffffff81671204>] SyS_ioctl+0x74/0x80 fs/ioctl.c:613
     [<ffffffff852a7876>] entry_SYSCALL_64_fastpath+0x16/0x7a

Reported-and-tested-by: Dmitry Vyukov <dvyukov at google.com>
Signed-off-by: Peter Hurley <peter at hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/net/irda/irtty-sir.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/drivers/net/irda/irtty-sir.c b/drivers/net/irda/irtty-sir.c
index 696852e..7a3f990 100644
--- a/drivers/net/irda/irtty-sir.c
+++ b/drivers/net/irda/irtty-sir.c
@@ -430,16 +430,6 @@ static int irtty_open(struct tty_struct *tty)

 	/* Module stuff handled via irda_ldisc.owner - Jean II */

-	/* First make sure we're not already connected. */
-	if (tty->disc_data != NULL) {
-		priv = tty->disc_data;
-		if (priv && priv->magic == IRTTY_MAGIC) {
-			ret = -EEXIST;
-			goto out;
-		}
-		tty->disc_data = NULL;		/* ### */
-	}
-
 	/* stop the underlying  driver */
 	irtty_stop_receiver(tty, TRUE);
 	if (tty->ops->stop)
--
2.7.4