[PATCH 0/3] add new strscpy() API for string copy

[Chris Metcalf]

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.

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.

This builds on an earlier version of strscpy() submitted as
a file-static method in the arch/tile/gxio tree last year, after
an attempt to gather interest in a new generic strscpy failed:

  https://lkml.org/lkml/2014/8/7/368

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() and strscpy_truncate()
  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               |   6 ++
 lib/string.c                         | 109 +++++++++++++++++++++++++++++++++++
 25 files changed, 212 insertions(+), 37 deletions(-)

-- 
2.1.2

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