linux-kernel - Re: [PATCH 27/33] sctp: export sctp_setsockopt

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Date:   Fri, 15 May 2020 17:24:59 +0200
From:   Christoph Hellwig <hch@....de>
To:     David Howells <dhowells@...hat.com>
Cc:     Christoph Hellwig <hch@....de>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-nvme@...ts.infradead.org, linux-sctp@...r.kernel.org,
        target-devel@...r.kernel.org, linux-afs@...ts.infradead.org,
        drbd-dev@...ts.linbit.com, linux-cifs@...r.kernel.org,
        rds-devel@....oracle.com, linux-rdma@...r.kernel.org,
        cluster-devel@...hat.com, Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        linux-block@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        ceph-devel@...r.kernel.org, linux-nfs@...r.kernel.org,
        Neil Horman <nhorman@...driver.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>,
        linux-kernel@...r.kernel.org, Jon Maloy <jmaloy@...hat.com>,
        Ying Xue <ying.xue@...driver.com>,
        "David S. Miller" <davem@...emloft.net>, ocfs2-devel@....oracle.com
Subject: Re: [PATCH 27/33] sctp: export sctp_setsockopt_bindx

On Fri, May 15, 2020 at 04:20:02PM +0100, David Howells wrote:
> Christoph Hellwig <hch@....de> 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.