[3.13.y-ckt stable] Patch "tty: Fix GPF in flush_to_ldisc()" has been added to the 3.13.y-ckt tree

[Kamal Mostafa]

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

    tty: Fix GPF in flush_to_ldisc()

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt33.

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

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From c090adb0c7995700b7bcfc5252aa2c2768f53906 Mon Sep 17 00:00:00 2001
From: Peter Hurley <peter at hurleysoftware.com>
Date: Fri, 27 Nov 2015 14:25:08 -0500
Subject: tty: Fix GPF in flush_to_ldisc()

commit 9ce119f318ba1a07c29149301f1544b6c4bea52a upstream.

A line discipline which does not define a receive_buf() method can
can cause a GPF if data is ever received [1]. Oddly, this was known
to the author of n_tracesink in 2011, but never fixed.

[1] GPF report
    BUG: unable to handle kernel NULL pointer dereference at           (null)
    IP: [<          (null)>]           (null)
    PGD 3752d067 PUD 37a7b067 PMD 0
    Oops: 0010 [#1] SMP KASAN
    Modules linked in:
    CPU: 2 PID: 148 Comm: kworker/u10:2 Not tainted 4.4.0-rc2+ #51
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
    Workqueue: events_unbound flush_to_ldisc
    task: ffff88006da94440 ti: ffff88006db60000 task.ti: ffff88006db60000
    RIP: 0010:[<0000000000000000>]  [<          (null)>]           (null)
    RSP: 0018:ffff88006db67b50  EFLAGS: 00010246
    RAX: 0000000000000102 RBX: ffff88003ab32f88 RCX: 0000000000000102
    RDX: 0000000000000000 RSI: ffff88003ab330a6 RDI: ffff88003aabd388
    RBP: ffff88006db67c48 R08: ffff88003ab32f9c R09: ffff88003ab31fb0
    R10: ffff88003ab32fa8 R11: 0000000000000000 R12: dffffc0000000000
    R13: ffff88006db67c20 R14: ffffffff863df820 R15: ffff88003ab31fb8
    FS:  0000000000000000(0000) GS:ffff88006dc00000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    CR2: 0000000000000000 CR3: 0000000037938000 CR4: 00000000000006e0
    Stack:
     ffffffff829f46f1 ffff88006da94bf8 ffff88006da94bf8 0000000000000000
     ffff88003ab31fb0 ffff88003aabd438 ffff88003ab31ff8 ffff88006430fd90
     ffff88003ab32f9c ffffed0007557a87 1ffff1000db6cf78 ffff88003ab32078
    Call Trace:
     [<ffffffff8127cf91>] process_one_work+0x8f1/0x17a0 kernel/workqueue.c:2030
     [<ffffffff8127df14>] worker_thread+0xd4/0x1180 kernel/workqueue.c:2162
     [<ffffffff8128faaf>] kthread+0x1cf/0x270 drivers/block/aoe/aoecmd.c:1302
     [<ffffffff852a7c2f>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468
    Code:  Bad RIP value.
    RIP  [<          (null)>]           (null)
     RSP <ffff88006db67b50>
    CR2: 0000000000000000
    ---[ end trace a587f8947e54d6ea ]---

Reported-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/tty/tty_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 4847fc5..bb8fc8e 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -414,7 +414,7 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
 		count = disc->ops->receive_buf2(tty, p, f, count);
 	else {
 		count = min_t(int, count, tty->receive_room);
-		if (count)
+		if (count && disc->ops->receive_buf)
 			disc->ops->receive_buf(tty, p, f, count);
 	}
 	head->read += count;
--
1.9.1