linux-kernel - Re: [GIT PULL] TTY/Serial driver fixes for 4.11-rc4

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Date:   Thu, 13 Apr 2017 09:07:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Vegard Nossum <vegard.nossum@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>
Subject: Re: [GIT PULL] TTY/Serial driver fixes for 4.11-rc4

On Thu, Apr 13, 2017 at 3:50 AM, Vegard Nossum <vegard.nossum@...il.com> wrote:
>
> I've bisected a syzkaller crash down to this commit
> (5362544bebe85071188dd9e479b5a5040841c895). The crash is:
>
> [   25.137552] BUG: unable to handle kernel paging request at 0000000000002280
> [   25.137579] IP: mutex_lock_interruptible+0xb/0x30

It would seem to be the

                if (mutex_lock_interruptible(&ldata->atomic_read_lock))

call in n_tty_read(), the offset is about right for a NULL 'ldata'
pointer (it's a big structure, it has a couple of character buffers of
size N_TTY_BUF_SIZE).

I don't see the obvious fix, so I suspect at this point we should just
revert, as that commit seems to introduce worse problems that it is
supposed to fix. Greg?

              Linus