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Message-Id: <20120406141936.25d68860.akpm@linux-foundation.org>
Date: Fri, 6 Apr 2012 14:19:36 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Will Drewry <wad@...omium.org>
Cc: linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
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luto@....edu, eparis@...hat.com, serge.hallyn@...onical.com,
djm@...drot.org, scarybeasts@...il.com, indan@....nu, pmoore@...hat.com,
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coreyb@...ux.vnet.ibm.com, keescook@...omium.org, jmorris@...ei.org
Subject: Re: [PATCH v17 10/15] seccomp: add SECCOMP_RET_ERRNO
On Thu, 29 Mar 2012 15:01:55 -0500
Will Drewry <wad@...omium.org> wrote:
> This change adds the SECCOMP_RET_ERRNO as a valid return value from a
> seccomp filter. Additionally, it makes the first use of the lower
> 16-bits for storing a filter-supplied errno. 16-bits is more than
> enough for the errno-base.h calls.
>
> Returning errors instead of immediately terminating processes that
> violate seccomp policy allow for broader use of this functionality
> for kernel attack surface reduction. For example, a linux container
> could maintain a whitelist of pre-existing system calls but drop
> all new ones with errnos. This would keep a logically static attack
> surface while providing errnos that may allow for graceful failure
> without the downside of do_exit() on a bad call.
>
>
> ...
>
> @@ -64,11 +65,17 @@ struct seccomp {
> struct seccomp_filter *filter;
> };
>
> -extern void __secure_computing(int);
> -static inline void secure_computing(int this_syscall)
> +/*
> + * Direct callers to __secure_computing should be updated as
> + * CONFIG_HAVE_ARCH_SECCOMP_FILTER propagates.
Are there any such callers? There's one I see in arm, but it's called
from assembly code.
> + */
> +extern void __secure_computing(int) __deprecated;
> +extern int __secure_computing_int(int);
> +static inline int secure_computing(int this_syscall)
> {
> if (unlikely(test_thread_flag(TIF_SECCOMP)))
> - __secure_computing(this_syscall);
> + return __secure_computing_int(this_syscall);
> + return 0;
> }
>
> ...
>
> void __secure_computing(int this_syscall)
> {
> + /* Filter calls should never use this function. */
> + BUG_ON(current->seccomp.mode == SECCOMP_MODE_FILTER);
> + __secure_computing_int(this_syscall);
> +}
> +
> +int __secure_computing_int(int this_syscall)
What the heck does "_int" mean here? I read it as "integer" but
perhaps it's shorthand for "internal". Give us a better name, please.
Or a code comment.
> +{
> int mode = current->seccomp.mode;
> int exit_sig = 0;
> int *syscall;
> + u32 ret = SECCOMP_RET_KILL;
> + int data;
>
> switch (mode) {
> case SECCOMP_MODE_STRICT:
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