linux-kernel - Re: [PATCH printk 2/3] printk: move dictionary keys to dev_printk

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Date:   Fri, 18 Sep 2020 14:13:42 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk 2/3] printk: move dictionary keys to
 dev_printk_info

On Fri 2020-09-18 08:16:37, Rasmus Villemoes wrote:
> On 17/09/2020 15.16, John Ogness wrote:
> 
> >  	if (dev->class)
> >  		subsys = dev->class->name;
> >  	else if (dev->bus)
> >  		subsys = dev->bus->name;
> >  	else
> > -		return 0;
> > +		return;
> >  
> > -	pos += snprintf(hdr + pos, hdrlen - pos, "SUBSYSTEM=%s", subsys);
> > -	if (pos >= hdrlen)
> > -		goto overflow;
> > +	snprintf(dev_info->subsystem, sizeof(dev_info->subsystem), subsys);
> 
> It's unlikely that subsys would contain a %, but this will be yet
> another place to spend brain cycles ignoring if doing static analysis.
> So can we not do this. Either of strXcpy() for X=s,l will do the same
> thing, and likely faster.

Good point! Better be on the safe size in a generic printk() API.

Well, I am afraid that this would be only small drop in a huge lake.
class->name and bus->name seems to be passed to %s in so many
*print*() calls all over the kernel code.

IMHO, this is not the right place to prevent the problem. Dangerous
names must be prevented when a new bus, class, device is added.

Best Rergards,
Petr