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From: Kees Cook <keescook@chromium.org>
Date: Fri, 14 Jul 2017 16:51:31 -0700
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Subject: Re: [PATCH] replace incorrect strscpy use in FORTIFY_SOURCE
To: Daniel Micay <danielmicay@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Dave Jones <davej@codemonkey.org.uk>,
        Anna Schumaker <schumaker.anna@gmail.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
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On Fri, Jul 14, 2017 at 2:28 PM, Daniel Micay <danielmicay@gmail.com> wrote:
> Using strscpy was wrong because FORTIFY_SOURCE is passing the maximum
> possible size of the outermost object, but strscpy defines the count
> parameter as the exact buffer size, so this could copy past the end of
> the source. This would still be wrong with the planned usage of
> __builtin_object_size(p, 1) for intra-object overflow checks since it's
> the maximum possible size of the specified object with no guarantee of
> it being that large.
>
> Reuse of the fortified functions like this currently makes the runtime
> error reporting less precise but that can be improved later on.
>
> Signed-off-by: Daniel Micay <danielmicay@gmail.com>

Thanks for fixing this! Linus, do you want to take this directly or
have it go via -mm where fortify landed originally?

Acked-by: Kees Cook <keescook@chromium.org>

As far as testing goes, was the NFS tree not in -next, or was a test
not running against -next? I'm curious why it took until the NFS tree
landed in Linus's tree for this to get noticed. Fortify was in -next
for a while...

-Kees

-- 
Kees Cook
Pixel Security