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Date: Sun, 19 Apr 2015 09:32:16 +0200 From: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> To: Kees Cook <keescook@...omium.org> Cc: "linux-man@...r.kernel.org" <linux-man@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>, Pierre Chifflier <pollux@...ian.org> Subject: Re: [patch] seccomp.2: Note that memory area is read-only On 19 April 2015 at 01:37, Kees Cook <keescook@...omium.org> wrote: > On Mon, Apr 6, 2015 at 8:29 AM, Michael Kerrisk (man-pages) > <mtk.manpages@...il.com> 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! 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 <linux/audit.h>) */ >> >> >> -- >> 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 -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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