linux-kernel - Re: [PATCH v2 1/1] lib/string: Add strscpy

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Message-ID: <20190225213109.GB5177@eros.localdomain>
Date:   Tue, 26 Feb 2019 08:31:09 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Tobin C. Harding" <tobin@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andy Lutomirski <luto@...capital.net>,
        Daniel Micay <danielmicay@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Shuah Khan <shuah@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] lib/string: Add strscpy_pad() function

On Mon, Feb 25, 2019 at 10:19:47AM +0200, Andy Shevchenko wrote:
> On Mon, Feb 25, 2019 at 6:17 AM 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.
> >
> > Add test module for the new code.
> 
> > --- /dev/null
> > +++ b/lib/test_strscpy.c
> > @@ -0,0 +1,175 @@
> 
> > +// SPDX-License-Identifier: GPL-2.0
> 
> > +MODULE_LICENSE("GPL");
> 
> License mismatch.

Thanks, will re-spin with 

  // SPDX-License-Identifier: GPL-2.0+

> Do we need a separate module for this test?

Separate as in not in lib/test_string.h?  I intend on moving the test
into that file once I've done some cleanup in tools/testing/selftest/lib/

I also tried to do this without using a module using
tools/testing/selftest/kselftest_harness.h but I could not get the
compiler to see read the patched version of
linux/include/linux/string.h?

Related question if you feel like answering it; why are test modules for
lib/ in lib/ and not in tools/testing/?

Very much open to suggestions on current best practices for kernel testing.

thanks,
Tobin.