Re: [PATCH v2 1/2] sctp: export sctp_endpoint_{hold,put}() and return incremented endpoint

On Fri, 17 Dec 2021 13:46:06 +0000 Lee Jones wrote:

For example, in sctp_sock_dump(), we could have the following hunk:

	sctp_endpoint_hold(tsp->asoc->ep);
	ep = tsp->asoc->ep;
	sk = ep->base.sk
	lock_sock(ep->base.sk);

It is possible for this task to be swapped out immediately following
the call into sctp_endpoint_hold() that would change the address of
tsp->asoc->ep to point to a completely different endpoint.  This means
a reference could be taken to the old endpoint and the new one would
be processed without a reference taken, moreover the new endpoint
could then be freed whilst still processing as a result, causing a
use-after-free.

If we return the exact pointer that was held, we ensure this task
processes only the endpoint we have taken a reference to.  The
resultant hunk now looks like this:

      ep = sctp_endpoint_hold(tsp->asoc->ep);
	sk = ep->base.sk
	lock_sock(sk);

If you have to explain what the next patch will do to make sense 
of this one it really is better to merge the two patches.
Exporting something is not a functional change, nor does it make
the changes easier to review, in fact the opposite is true.

Fixes: 8f840e47f190c ("sctp: add the sctp_diag.c file")

This patch in itself fixes exactly nothing.