On Tue, Jul 28, 2020 at 10:07 AM David Laight [off-list ref] wrote:

From: Christoph Hellwig

quoted

Sent: 27 July 2020 17:24

On Mon, Jul 27, 2020 at 06:16:32PM +0200, Jason A. Donenfeld wrote:

quoted

Maybe sockptr_advance should have some safety checks and sometimes
return -EFAULT? Or you should always use the implementation where
being a kernel address is an explicit bit of sockptr_t, rather than
being implicit?

I already have a patch to use access_ok to check the whole range in
init_user_sockptr.

That doesn't make (much) difference to the code paths that ignore
the user-supplied length.
OTOH doing the user/kernel check on the base address (not an
incremented one) means that the correct copy function is always
selected.

Right, I had the same reaction in reading this, but actually, his code
gets rid of the sockptr_advance stuff entirely and never mutates, so
even though my point about attacking those pointers was missed, the
code does the better thing now -- checking the base address and never
mutating the pointer. So I think we're good.

Perhaps the functions should all be passed a 'const sockptr_t'.
The typedef could be made 'const' - requiring non-const items
explicitly use the union/struct itself.

I was thinking the same, but just by making the pointers inside the
struct const. However, making the whole struct const via the typedef
is a much better idea. That'd probably require changing the signature
of init_user_sockptr a bit, which would be fine, but indeed I think
this would be a very positive change.

Jason