linux-kernel - Re: [PATCH 2/3] string: provide strscpy() and strscpy

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Date:	Thu, 7 May 2015 11:10:55 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Fabian Frederick <fabf@...net.be>,
	Randy Dunlap <rdunlap@...radead.org>,
	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Greg KH <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"David S. Miller" <davem@...emloft.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Theodore Ts'o <tytso@....edu>,
	Grant Likely <grant.likely@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 2/3] string: provide strscpy() and strscpy_truncate()

On 05/07/2015 05:00 AM, Dan Carpenter wrote:
> On Wed, May 06, 2015 at 06:45:56PM +0200, Geert Uytterhoeven wrote:
>> On Wed, May 6, 2015 at 5:59 PM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
>>> We actually do have a __must_check tag so it's easy enough to force
>>> people to check.  A different option is we could make it trigger a
>> People tend to ignore compiler warnings...
> We're doing a lot better these days with zero day build testing.  There
> is not even one ignored __must_check return in my allmodconfig.

If we keep the strscpy/strscpy_truncate distinction, I agree that having
__must_check on strscpy seems like a good idea.

>>> WARN_ONCE().
>>>
>>> #define strXcpy(dest, src, len) (({                             \
>>>          ssize_t __ret = strscpy_truncate(dest, src, len);       \
>>>          WARN_ONCE(__ret < 0, "strXcpy trancates\n");            \
>>>          __ret; }))
>> Which will probably trigger only in extreme cases in the wild, not during
>> development.
> It's less subtle than just putting an empty string there so we're more
> likely to get bug reports than with the original code.

The problem with WARN_ONCE() here is that we may be using strscpy()
to take user input of some kind.  If so, we don't want to warn if we
are truncating the string - we just want to return a suitable error up
the call stack.

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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