On 11/14/18 8:39 AM, Christoph Hellwig wrote:

On Wed, Nov 14, 2018 at 08:33:06AM -0700, Jens Axboe wrote:

quoted

It's measurable. It doesn't defeat the const at all, the mq_ops
is still const and is never modified outside of when the queue
is allocated. The only difference is of course that it is no
longer residing in a read only mapped section, which is a shame.

And the separate section is very much the point of the const.

Without it attackers can easily overwrite the function pointer and
use it for exploits, as the C const attribute by itself doesn't
protect from that in any way.  But once it is in a read-only section
it can't easily be modified.

Are we really worried about this as an attack surface? I get it
for other types of ops, but for mq_ops, I'd be more worried about
callers changing it inadvertently, and they still can't do that.

It's not a huge deal to me, I can drop this one for now and
revisit at a later time.

-- 
Jens Axboe