linux-kernel - [PATCH v2 0/3] add new strscpy() API for string copy

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Message-ID: <1436386845-11989-1-git-send-email-cmetcalf@ezchip.com>
Date:	Wed, 8 Jul 2015 16:20:42 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Chris Metcalf <cmetcalf@...hip.com>,
	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>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	<linux-arch@...r.kernel.org>
Subject: [PATCH v2 0/3] add new strscpy() API for string copy

v2: eliminate strscpy_truncate(); the single strscpy() API in v2
  just tolerates a truncated string (while returning an error value)
  Also, improve some of the comparison language with strlcpy/strncpy.

This patch series addresses limitations in strncpy() and strlcpy();
both the old APIs are unpleasant, as Linus nicely summarized here:

  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, doesn't walk past the
requested copy size on the source string, 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.

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.

The patch series is available to be pulled from

  git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile.git strscpy

Chris Metcalf (3):
  Make asm/word-at-a-time.h available on all architectures
  string: provide strscpy()
  tile: use global strscpy() rather than private copy

 arch/arc/include/asm/Kbuild          |  1 +
 arch/avr32/include/asm/Kbuild        |  1 +
 arch/blackfin/include/asm/Kbuild     |  1 +
 arch/c6x/include/asm/Kbuild          |  1 +
 arch/cris/include/asm/Kbuild         |  1 +
 arch/frv/include/asm/Kbuild          |  1 +
 arch/hexagon/include/asm/Kbuild      |  1 +
 arch/ia64/include/asm/Kbuild         |  1 +
 arch/m32r/include/asm/Kbuild         |  1 +
 arch/metag/include/asm/Kbuild        |  1 +
 arch/microblaze/include/asm/Kbuild   |  1 +
 arch/mips/include/asm/Kbuild         |  1 +
 arch/mn10300/include/asm/Kbuild      |  1 +
 arch/nios2/include/asm/Kbuild        |  1 +
 arch/powerpc/include/asm/Kbuild      |  1 +
 arch/s390/include/asm/Kbuild         |  1 +
 arch/score/include/asm/Kbuild        |  1 +
 arch/tile/gxio/mpipe.c               | 33 ++------------
 arch/tile/include/asm/Kbuild         |  1 +
 arch/um/include/asm/Kbuild           |  1 +
 arch/unicore32/include/asm/Kbuild    |  1 +
 arch/xtensa/include/asm/Kbuild       |  1 +
 include/asm-generic/word-at-a-time.h | 80 ++++++++++++++++++++++++++++----
 include/linux/string.h               |  3 ++
 lib/string.c                         | 88 ++++++++++++++++++++++++++++++++++++
 25 files changed, 188 insertions(+), 37 deletions(-)

-- 
2.1.2

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