linux-kernel - [RFC 0/3] eliminate potential race in string() (was: [PATCH] string: Improve the generic strlcpy() implementation)

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Message-ID: <87r3l4wgom.fsf_-_@rasmusvillemoes.dk>
Date:	Fri, 09 Oct 2015 11:10:33 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...hip.com>,
	open list <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>
Subject: [RFC 0/3] eliminate potential race in string() (was: [PATCH] string: Improve the generic strlcpy() implementation)

On Fri, Oct 09 2015, Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> It's hard not to agree with the overall "let's make it more robust if it
> can be done sanely+cheaply+cleanly". I was a bit skeptical about whether
> those three requirements could be met, since we'd have to do
> byte-by-byte traversal of the string, maybe-copying it to the output as
> we go along, but then right-alignment would require us to do a memmove,
> but not before we've done some complicated bookkeeping
> exercise. However, now that I read the source again, it seems that Al
> Viro already did that exercise when he added dentry(). So maybe it's
> doable without a net increase in LOC.

Something like this. The net increase is because I added a
comment. Passes the new printf test suite, but I'm not sure that's
thorough enough yet - still, it's better than nothing. There's also this
small bonus:

$ scripts/bloat-o-meter /tmp/vsprintf.o.{old,new}
add/remove: 1/0 grow/shrink: 0/2 up/down: 178/-245 (-67)
function                                     old     new   delta
widen_string.isra                              -     178    +178
string.isra                                  186     109     -77
dentry_name.isra                             358     190    -168


Rasmus Villemoes (3):
  lib/vsprintf.c: pull out padding code from dentry_name()
  lib/vsprintf.c: move string() below widen_string()
  lib/vsprintf.c: eliminate potential race in string()

 lib/vsprintf.c | 98 +++++++++++++++++++++++++++++++---------------------------
 1 file changed, 52 insertions(+), 46 deletions(-)

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