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Date: Tue, 21 Feb 2012 14:41:28 -0800
From: Kees Cook <keescook@...omium.org>
To: Will Drewry <wad@...omium.org>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
davem@...emloft.net, hpa@...or.com, mingo@...hat.com, oleg@...hat.com,
peterz@...radead.org, rdunlap@...otime.net, mcgrathr@...omium.org,
tglx@...utronix.de, luto@....edu, eparis@...hat.com,
serge.hallyn@...onical.com, djm@...drot.org, scarybeasts@...il.com,
indan@....nu, pmoore@...hat.com, akpm@...ux-foundation.org,
corbet@....net, eric.dumazet@...il.com, markus@...omium.org
Subject: Re: [PATCH v10 06/11] seccomp: add SECCOMP_RET_ERRNO
On Tue, Feb 21, 2012 at 11:30:30AM -0600, Will Drewry wrote:
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 0043b7e..23f1844 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -136,22 +136,18 @@ static void *bpf_load(const void *nr, int off, unsigned int size, void *buf)
> static u32 seccomp_run_filters(int syscall)
> {
> struct seccomp_filter *f;
> - u32 ret = SECCOMP_RET_KILL;
> static const struct bpf_load_fn fns = {
> bpf_load,
> sizeof(struct seccomp_data),
> };
> + u32 ret = SECCOMP_RET_ALLOW;
> const void *sc_ptr = (const void *)(uintptr_t)syscall;
> -
> /*
> * All filters are evaluated in order of youngest to oldest. The lowest
> * BPF return value always takes priority.
> */
> - for (f = current->seccomp.filter; f; f = f->prev) {
> - ret = bpf_run_filter(sc_ptr, f->insns, &fns);
> - if (ret != SECCOMP_RET_ALLOW)
> - break;
> - }
> + for (f = current->seccomp.filter; f; f = f->prev)
> + ret = min_t(u32, ret, bpf_run_filter(sc_ptr, f->insns, &fns));
> return ret;
> }
I'd like to see this fail closed in the (theoretically impossible, but
why risk it) case of there being no filters at all. Could do something
like this:
u32 ret = current->seccomp.filter ? SECCOMP_RET_ALLOW : SECCOMP_RET_KILL;
Or, just this, to catch the misbehavior:
if (unlikely(current->seccomp.filter == NULL))
return SECCOMP_RET_KILL;
-Kees
--
Kees Cook
ChromeOS Security
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