Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET_ERRNO
From: Kees Cook
Date: Sat Feb 25 2012 - 15:20:25 EST
On Fri, Feb 24, 2012 at 7:21 PM, Will Drewry <wad@xxxxxxxxxxxx> 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.
>
> v11: - check for NULL filter (keescook@xxxxxxxxxxxx)
> v10: - change loaders to fn
> v9: - n/a
> v8: - update Kconfig to note new need for syscall_set_return_value.
> - reordered such that TRAP behavior follows on later.
> - made the for loop a little less indent-y
> v7: - introduced
>
> Signed-off-by: Will Drewry <wad@xxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> + /* Ensure unexpected behavior doesn't result in failing open. */
> + if (unlikely(current->seccomp.filter == NULL))
> + ret = SECCOMP_RET_KILL;
Any reason to not just immediately return in this case?
-Kees
--
Kees Cook
ChromeOS Security
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