From: Petr Mladek <pmladek@suse.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, Qian Cai <cai@gmx.us>,
linux-kernel@vger.kernel.org, "Tobin C. Harding" <me@tobin.cc>,
Geert Uytterhoeven <geert+renesas@glider.be>,
Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Subject: Re: WARNING: CPU: 26 PID: 64391 at lib/vsprintf.c:2193 set_precision+0x84/0x90
Date: Wed, 14 Nov 2018 20:29:32 +0100 [thread overview]
Message-ID: <20181114192932.uir4fuuteer7bqtm@pathway.suse.cz> (raw)
In-Reply-To: <20181114093819.GL10650@smile.fi.intel.com>
On Wed 2018-11-14 11:38:19, Andy Shevchenko wrote:
> On Wed, Nov 14, 2018 at 12:05:12AM +0100, Petr Mladek wrote:
> > On Tue 2018-11-13 14:23:17, Steven Rostedt wrote:
> > > On Tue, 13 Nov 2018 13:58:18 -0500
> > > Qian Cai <cai@gmx.us> wrote:
> > >
> > > > > Care to print the len and name parameters before this line?
> > > > len = 60612; name =
> > >
> > > How big are pages on arm64? Because we shouldn't get to this path if
> > > the string is bigger than PAGE_SIZE. But I know that on PPC64,
> > > PAGE_SIZE can be 64K, and 60612 is less than that. Thus, if we get
> > > there, the test is against signed int:16 (16 bit signed integer) that
> > > can go up to most 32768. If the string size is bigger than that, you
> > > would get this error.
> > >
> > > I would just say to ignore it.
> >
> > I tend to agree.
> >
> > > The only thing that can happen if
> > > someone does this is to trigger the warning. Unless if it is considered
> > > a form of DOS, where userspace just bombards the console by triggering
> > > this waring.
> >
> > We are actually on the safe side because it is WARN_ONCE().
> >
> > > But I don't see a problem with the actual design. There's
> > > no reason we should be processing string variables bigger than 32768 in
> > > vsprintf.
> >
> > It is not even needed in this case. The string is limited also by
> > MODULE_NAME_LEN.
>
> At least not in this code.
>
> Are you proposing to replace strlen(name) with strnlen(name, MODULE_NAME_LEN)?
It might be a solution. Well, it looks like a wrong design when we
would need to use MODULE_NAME_LEN outside module loader code. Also
it does not handle other request_module() users that might be
affected.
On the other hand, I am not sure how a proper solution would look
like. request_module() should not limit printk format before
the arguments are substituted.
The most clean solution probably would be on the vsprintf-level.
I mean to limit the precision by the overall string length
limit. But it looks a bit weird as well.
I still tend to ignore it. The code is safe from the security point of
view. The warning would trigger only when completely misused.
Best Regards,
Petr
next prev parent reply other threads:[~2018-11-14 19:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-13 16:55 WARNING: CPU: 26 PID: 64391 at lib/vsprintf.c:2193 set_precision+0x84/0x90 Qian Cai
2018-11-13 17:20 ` Geert Uytterhoeven
2018-11-13 17:32 ` Andy Shevchenko
2018-11-13 17:29 ` Andy Shevchenko
2018-11-13 18:58 ` Qian Cai
2018-11-13 19:23 ` Steven Rostedt
2018-11-13 23:05 ` Petr Mladek
2018-11-14 9:38 ` Andy Shevchenko
2018-11-14 19:29 ` Petr Mladek [this message]
2018-11-14 20:35 ` Qian Cai
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