Patch "wan/x25: Fix use-after-free in x25_asy_open_tty()" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

    wan/x25: Fix use-after-free in x25_asy_open_tty()

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     wan-x25-fix-use-after-free-in-x25_asy_open_tty.patch

and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Peter Hurley <[email protected]>
Date: Fri, 27 Nov 2015 14:18:39 -0500
Subject: wan/x25: Fix use-after-free in x25_asy_open_tty()

From: Peter Hurley <[email protected]>

commit ee9159ddce14bc1dec9435ae4e3bd3153e783706 upstream.

The N_X25 line discipline may access the previous line discipline's closed and already-freed 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]

    [  634.336761] ==================================================================
    [  634.338226] BUG: KASAN: use-after-free in x25_asy_open_tty+0x13d/0x490 at addr ffff8800a743efd0
    [  634.339558] Read of size 4 by task syzkaller_execu/8981
    [  634.340359] =============================================================================
    [  634.341598] BUG kmalloc-512 (Not tainted): kasan: bad access detected
    ...
    [  634.405018] Call Trace:
    [  634.405277] dump_stack (lib/dump_stack.c:52)
    [  634.405775] print_trailer (mm/slub.c:655)
    [  634.406361] object_err (mm/slub.c:662)
    [  634.406824] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236)
    [  634.409581] __asan_report_load4_noabort (mm/kasan/report.c:279)
    [  634.411355] x25_asy_open_tty (drivers/net/wan/x25_asy.c:559 (discriminator 1))
    [  634.413997] tty_ldisc_open.isra.2 (drivers/tty/tty_ldisc.c:447)
    [  634.414549] tty_set_ldisc (drivers/tty/tty_ldisc.c:567)
    [  634.415057] tty_ioctl (drivers/tty/tty_io.c:2646 drivers/tty/tty_io.c:2879)
    [  634.423524] do_vfs_ioctl (fs/ioctl.c:43 fs/ioctl.c:607)
    [  634.427491] SyS_ioctl (fs/ioctl.c:622 fs/ioctl.c:613)
    [  634.427945] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:188)

---
 drivers/net/wan/x25_asy.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

@@ -545,16 +545,12 @@ static void x25_asy_receive_buf(struct t
 
 static int x25_asy_open_tty(struct tty_struct *tty)
 {
-	struct x25_asy *sl = tty->disc_data;
+	struct x25_asy *sl;
 	int err;
 
 	if (tty->ops->write == NULL)
 		return -EOPNOTSUPP;
 
-	/* First make sure we're not already connected. */
-	if (sl && sl->magic == X25_ASY_MAGIC)
-		return -EEXIST;
-
 	/* OK.  Find a free X.25 channel to use. */
 	sl = x25_asy_alloc();
 	if (sl == NULL)

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/staging-speakup-use-tty_ldisc_ref-for-paste-kworker.patch queue-3.14/wan-x25-fix-use-after-free-in-x25_asy_open_tty.patch queue-3.14/pty-make-sure-super_block-is-still-valid-in-final-dev-tty-close.patch queue-3.14/pty-fix-possible-use-after-free-of-tty-driver_data.patch