Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752453AbbDRXhi (ORCPT ); Sat, 18 Apr 2015 19:37:38 -0400 Received: from mail-vn0-f53.google.com ([209.85.216.53]:46020 "EHLO mail-vn0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751039AbbDRXhg (ORCPT ); Sat, 18 Apr 2015 19:37:36 -0400 MIME-Version: 1.0 In-Reply-To: <5522A66F.9060606@gmail.com> References: <5522A66F.9060606@gmail.com> Date: Sat, 18 Apr 2015 16:37:35 -0700 X-Google-Sender-Auth: z4W1HRFLsojbN-4wa9jnvxRq3uc Message-ID: Subject: Re: [patch] seccomp.2: Note that memory area is read-only From: Kees Cook To: "Michael Kerrisk (man-pages)" Cc: "linux-man@vger.kernel.org" , lkml Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1882 Lines: 63 On Mon, Apr 6, 2015 at 8:29 AM, Michael Kerrisk (man-pages) wrote: > Hi Kees, > > I recently was asked about the point below, and had to go check the code > to be sure, since the man page said nothing. It would be good to have > a confirmation: the seccomp_data buffer supplied to a seccomp BPF program > is read-only, right? (That is, one can't write to the buffer in order to > change the arguments that a system call actually receives.) That's correct. If BPF even allows changing the data, it's not copied back to the syscall when it runs. Anything wanting to do things like that would need to use ptrace to catch the call an directly modify the registers before continuing with the call. > > A small man page patch below. Looks good, thanks! -Kees > > Cheers, > > Michael > > --- a/man2/seccomp.2 > +++ b/man2/seccomp.2 > @@ -232,15 +232,15 @@ struct sock_filter { /* Filter block */ > }; > .fi > .in > > When executing the instructions, the BPF program operates on the > system call information made available (i.e., use the > .BR BPF_ABS > -addressing mode) as a buffer of the following form: > +addressing mode) as a (read-only) buffer of the following form: > > .in +4n > .nf > struct seccomp_data { > int nr; /* System call number */ > __u32 arch; /* AUDIT_ARCH_* value > (see ) */ > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/