linux-kernel - Re: [PATCH 6/6] lib: Add function strscpy_from

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Date:   Wed, 20 Feb 2019 08:53:45 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Jann Horn <jannh@...gle.com>
Cc:     "Tobin C. Harding" <tobin@...nel.org>,
        Kees Cook <keescook@...omium.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>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] lib: Add function strscpy_from_user()

On Tue, Feb 19, 2019 at 03:12:33AM +0100, Jann Horn wrote:
> On Tue, Feb 19, 2019 at 12:25 AM Tobin C. Harding <tobin@...nel.org> wrote:
> > Currently we have strncpy_from_userspace().  If the user string is
> > longer than the destination kernel buffer we get an error code -EFAULT.
> > We are unable to recover from here because this is the same error
> > returned if the access to userspace fails totally.
> >
> > There is no reason we cannot continue execution with the user string
> > truncated.
> >
> > Add a function strscpy_from_user() that guarantees the string written is
> > null-terminated.  If user string is longer than destination buffer
> > truncates the string.  Returns the number of characters written
> > excluding the null-terminator.
> >
> > Signed-off-by: Tobin C. Harding <tobin@...nel.org>
> > ---
> >  lib/strncpy_from_user.c | 43 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 43 insertions(+)
> >
> > diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
> > index 11fe9a4a00fd..6bd603ccec7a 100644
> > --- a/lib/strncpy_from_user.c
> > +++ b/lib/strncpy_from_user.c
> 
> This file is only built when CONFIG_GENERIC_STRNCPY_FROM_USER is set.
> Some architectures have their own versions of strncpy_from_user() and
> don't set that, so on those architectures, your code wouldn't be built
> into the kernel.

thanks!  Dropping *_from_user() stuff from set.

	Tobin