linux-kernel - Re: [PATCH 0/3] add new strscpy() API for string copy

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Date:	Fri, 15 May 2015 09:10:18 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Chris Metcalf <cmetcalf@...hip.com>
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>,
	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@...r.kernel.org
Subject: Re: [PATCH 0/3] add new strscpy() API for string copy

On Thu, 2015-04-30 at 12:01 -0400, Chris Metcalf wrote:
> This patch series addresses limitations in strncpy() and strlcpy();
> both the old APIs are unpleasant, as Linus nicely summarized here
> a couple of days ago:
> 
>   https://lkml.org/lkml/2015/4/28/570
> 
> and of course as other folks (Greg K-H and Linus again) said last year:
> 
>   https://plus.google.com/+gregkroahhartman/posts/1amLbuhWbh5
> 
> The proposed new API (strscpy(), for "s"afe string copy) has an
> easy-to-use API for detecting buffer overflow, avoids unsafe truncation
> by default, and isn't subject to thread-safety attacks like the current
> strlcpy implementation.  See patch 2/3 for more on why strscpy() is a
> good thing.

+1 on the concept.

> To make strscpy() work more efficiently I did the minimum tweaking
> necessary to allow <asm/word-at-a-time.h> to work on all architectures,
> though of course individual maintainers can still make their versions
> more efficient as needed.
> 
> It's likely not necessary for per-architecture implementations of
> strscpy() to be written, but I stuck with the standard __HAVE_ARCH_XXX
> model just for consistency with the rest of <linux/string.h>.
> 
> I tested the implementation with a simple user-space harness, so I
> believe it is correct for the corner cases I could think of.  In
> particular I pairwise-tested all the unaligned values of source and
> dest, and tested the restriction on src page-crossing at all
> unaligned offsets approaching the page boundary.

Can you please put that in tools/testing/selftests and merge it as part of the
series? That way I can run the tests and be confident it works on powerpc.

cheers


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