kernel-hardening - Re: [PATCH 4/6] lib/string: Add string copy/zero function

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Message-ID: <CAHp75VfO0SQ41zV1r3R2h2n2eRuGJzdsgHFzK7nRj85m7Xahgw@mail.gmail.com>
Date: Thu, 21 Feb 2019 14:02:57 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: "Tobin C. Harding" <tobin@...nel.org>, Shuah Khan <shuah@...nel.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org>, 
	Matthew Wilcox <willy@...radead.org>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Daniel Micay <danielmicay@...il.com>
Subject: Re: [PATCH 4/6] lib/string: Add string copy/zero function

On Thu, Feb 21, 2019 at 2:49 AM Kees Cook <keescook@...omium.org> wrote:
> On Mon, Feb 18, 2019 at 3:24 PM Tobin C. Harding <tobin@...nel.org> wrote:
> >
> > We have a function to copy strings safely and we have a function to copy
> > strings _and_ zero the tail of the destination (if source string is
> > shorter than destination buffer) but we do not have a function to do
> > both at once.  This means developers must write this themselves if they
> > desire this functionality.  This is a chore, and also leaves us open to
> > off by one errors unnecessarily.
> >
> > Add a function that calls strscpy() then memset()s the tail to zero if
> > the source string is shorter than the destination buffer.

> > +/* Wrapper function, no arch specific code required */
> > +ssize_t strscpy_zeroed(char *dest, const char *src, size_t count);
>
> bikeshed: I think "pad" is shorter and more descriptive. How about
> something like strspad() strscpy_pad() or strscpy_zero()? (just to
> shorten it slightly)

zero / zeroed examples in the kernel have semantics of getting some
area completely zeroed. OTOH pad means different and we have examples
as well (see seq_pad() as one).

So, I would definitely vote for _pad b/c of semantics.

-- 
With Best Regards,
Andy Shevchenko

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