linux-kernel - Re: [PATCH] seccomp: Use -1 marker for end of mode 1 syscall list

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Message-ID: <202006191253.B00874B22@keescook>
Date:   Fri, 19 Jun 2020 12:53:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Arnd Bergmann <arnd@...db.de>, Will Drewry <wad@...omium.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] seccomp: Use -1 marker for end of mode 1 syscall list

On Fri, Jun 19, 2020 at 12:42:14PM -0700, Andy Lutomirski wrote:
> On Fri, Jun 19, 2020 at 12:37 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > The terminator for the mode 1 syscalls list was a 0, but that could be
> > a valid syscall number (e.g. x86_64 __NR_read). By luck, __NR_read was
> > listed first and the loop construct would not test it, so there was no
> > bug. However, this is fragile. Replace the terminator with -1 instead,
> > and make the variable name for mode 1 syscall lists more descriptive.
> 
> Could the architecture instead supply the length of the list?

It could, but I didn't like the way the plumbing for that looked.

-- 
Kees Cook