linux-hardening - Re: [PATCH] x86/platform/uv: refactor deprecated strcpy and strncpy

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Date:   Wed, 23 Aug 2023 15:49:34 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Steve Wahl <steve.wahl@....com>, Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] x86/platform/uv: refactor deprecated strcpy and strncpy

On Wed, Aug 23, 2023 at 4:07 AM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Wed, Aug 23, 2023 at 1:32 AM Justin Stitt <justinstitt@...gle.com> wrote:
> >
> > Both `strncpy` and `strcpy` are deprecated for use on NUL-terminated
> > destination strings [1].
> >
> > A suitable replacement is `strscpy` [2] due to the fact that it
> > guarantees NUL-termination on its destination buffer argument which is
> > _not_ the case for `strncpy` or `strcpy`!
> >
> > In this case, we can drop both the forced NUL-termination and the `... -1` from:
> > |       strncpy(arg, val, ACTION_LEN - 1);
> > as `strscpy` implicitly has this behavior.
>
> ...
>
> >         char arg[ACTION_LEN], *p;
> >
> >         /* (remove possible '\n') */
> > -       strncpy(arg, val, ACTION_LEN - 1);
> > -       arg[ACTION_LEN - 1] = '\0';
> > +       strscpy(arg, val, ACTION_LEN);
> >         p = strchr(arg, '\n');
> >         if (p)
> >                 *p = '\0';
>
> https://lore.kernel.org/all/202212091545310085328@zte.com.cn/
>
> ...
>
> > +               strscpy(uv_nmi_action, arg, strlen(uv_nmi_action));
>
> strlen() on the destination?!
>
> ...
>
> > -                       strncpy(uv_nmi_action, "dump", strlen(uv_nmi_action));
> > +                       strscpy(uv_nmi_action, "dump", strlen(uv_nmi_action));
>
> Again, this is weird.

This is a common pattern with `strxcpy` and `sizeof` if you `$ rg
"strncpy\(.*sizeof"`. Do you recommend I switch the strlen(dest) to
strlen(src)? I only kept as-is because that's what was there
originally and I assumed some greater purpose of it.

>
> --
> With Best Regards,
> Andy Shevchenko