Re: [PATCH 27/33] sctp: export sctp_setsockopt_bindx

From: Christoph Hellwig
Date: Fri May 15 2020 - 11:25:10 EST


On Fri, May 15, 2020 at 04:20:02PM +0100, David Howells wrote:
> Christoph Hellwig <hch@xxxxxx> wrote:
>
> > > The advantage on using kernel_setsockopt here is that sctp module will
> > > only be loaded if dlm actually creates a SCTP socket. With this
> > > change, sctp will be loaded on setups that may not be actually using
> > > it. It's a quite big module and might expose the system.
> >
> > True. Not that the intent is to kill kernel space callers of setsockopt,
> > as I plan to remove the set_fs address space override used for it.
>
> For getsockopt, does it make sense to have the core kernel load optval/optlen
> into a buffer before calling the protocol driver? Then the driver need not
> see the userspace pointer at all.
>
> Similar could be done for setsockopt - allocate a buffer of the size requested
> by the user inside the kernel and pass it into the driver, then copy the data
> back afterwards.

I did look into that initially. The problem is that tons of sockopts
entirely ignore optlen and just use a fixed size. So I fear that there
could be tons of breakage if we suddently respect it. Otherwise that
would be a pretty nice way to handle the situation.