linux-kernel - Re: WARNING: CPU: 26 PID: 64391 at lib/vsprintf.c:2193 set

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Message-ID: <20181113230511.5di75uyht7ecdcvl@pathway.suse.cz>
Date:   Wed, 14 Nov 2018 00:05:12 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Qian Cai <cai@....us>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, "Tobin C. Harding" <me@...in.cc>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Subject: Re: WARNING: CPU: 26 PID: 64391 at lib/vsprintf.c:2193
 set_precision+0x84/0x90

On Tue 2018-11-13 14:23:17, Steven Rostedt wrote:
> On Tue, 13 Nov 2018 13:58:18 -0500
> Qian Cai <cai@....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.

Best Regards,
Petr