linux-kernel - Re: [PATCH] lib: vsprintf: check for NULL device_node name in device_node

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Date:   Thu, 18 Feb 2021 13:53:38 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        sergey.senozhatsky@...il.com, linux@...musvillemoes.dk,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH] lib: vsprintf: check for NULL device_node name in
 device_node_string()

On Wed 2021-02-17 15:50:00, Andy Shevchenko wrote:
> On Wed, Feb 17, 2021 at 01:15:43PM +0100, Enrico Weigelt, metux IT consult wrote:
> > Under rare circumstances it may happen that a device node's name is NULL
> > (most likely kernel bug in some other place).
> 
> What circumstances? How can I reproduce this? More information, please!
> 
> > In such situations anything
> > but helpful, if the debug printout crashes, and nobody knows what actually
> > happened here.
> > 
> > Therefore protect it by an explicit NULL check and print out an extra
> > warning.
> 
> ...
> 
> > +				pr_warn("device_node without name. Kernel bug ?\n");
> 
> If it's not once, then it's possible to have log spammed with this, right?
> 
> ...
> 
> > +				p = "<NULL>";
> 
> We have different standard de facto for NULL pointers to be printed. Actually
> if you wish, you may gather them under one definition (maybe somewhere under
> printk) and export to everybody to use.

Please, use

	if (check_pointer(&buf, end, p, spec))
		return buf;

It will print "(null)" instead of the name. It should be enough
to inform the user this way. The extra pr_warn() does not help
much to localize the problem anyway. And it is better to avoid
recursion in this path.

Best Regards,
Petr