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Subject[PATCH 3.2 08/70] tty: Fix GPF in flush_to_ldisc()
3.2.76-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Hurley <peter@hurleysoftware.com>

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@google.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -442,10 +442,12 @@ static void flush_to_ldisc(struct work_s
char_buf = head->char_buf_ptr + head->read;
flag_buf = head->flag_buf_ptr + head->read;
head->read += count;
- spin_unlock_irqrestore(&tty->buf.lock, flags);
- disc->ops->receive_buf(tty, char_buf,
+ if (disc->ops->receive_buf) {
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+ disc->ops->receive_buf(tty, char_buf,
flag_buf, count);
- spin_lock_irqsave(&tty->buf.lock, flags);
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ }
}
clear_bit(TTY_FLUSHING, &tty->flags);
}

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