From b23324ffa8ef8cc96865db76db938905d61d949a Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Fri, 27 Nov 2015 14:25:08 -0500 Subject: [PATCH] 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: [] process_one_work+0x8f1/0x17a0 kernel/workqueue.c:2030 [] worker_thread+0xd4/0x1180 kernel/workqueue.c:2162 [] kthread+0x1cf/0x270 drivers/block/aoe/aoecmd.c:1302 [] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468 Code: Bad RIP value. RIP [< (null)>] (null) RSP CR2: 0000000000000000 ---[ end trace a587f8947e54d6ea ]--- Reported-by: Dmitry Vyukov Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- drivers/tty/tty_buffer.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 4f02f9ce05c5..a846618ee1cb 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -442,10 +442,12 @@ static void flush_to_ldisc(struct work_struct *work) 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); } -- 2.39.2