[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <14d57dba-e293-11c2-67b2-18313a3a9b34@cern.ch>
Date: Sun, 31 Jul 2016 15:26:41 +0200
From: Vincent Brillault <vincent.brillault@...n.ch>
To: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Petr Mladek <pmladek@...e.com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Kees Cook <keescook@...omium.org>,
Thierry Reding <treding@...dia.com>,
Geliang Tang <geliangtang@....com>, Tejun Heo <tj@...nel.org>,
Ivan Delalande <colona@...sta.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: kernel/printk/printk.c: Invalid access when buffer wraps around?
Dear Sergey,
> sorry for long reply. do you see this in practice?
No, I've only thought of the bug will trying to adapt this code to build
a separate cyclic buffer in a dedicated kernel module.
> the first printk()->console_unlock() to notice `seen_seq != log_next_seq`
> will wakeup a task from log_wait, sleeping on
> wait_event_interruptible(seq != log_next_seq)
Yes, but a task could be not waiting to read reading while still having
open /dev/kmsg (e.g. after having read it in O_NONBLOCK)
> so I believe your assumption here is that we wrap around and then fill up
> the log_buf again without waking up the klogd even once, correct?
>
> CPU0 CPU1
>
> console_lock();
> printk();
> ... devkmsg_read();
> printk();
> console_unlock();
>
> like the above?
Mmm, I did not think of such a case, which might be possible. I was more
thinking of a userland daemon reading the buffer (via /dev/kmsg) in
non-blocking mode and only pulling from time to time. I agree that this
is probably not seen often, which could explain why nobody can see it in
practice.
Thanks for your time,
Vincent Brillault
Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)
Powered by blists - more mailing lists