Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET_ERRNO

[Will Drewry]

On Sat, Feb 25, 2012 at 2:20 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> 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>

Thanks!

>> +       /* 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?

Not that I can think of. I can just have it bail here.
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