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Date: Fri, 15 May 2020 17:24:59 +0200
From: Christoph Hellwig <hch@lst.de>
To: David Howells <dhowells@redhat.com>
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Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
	linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
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	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
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	Eric Dumazet <edumazet@google.com>,
	Jon Maloy <jmaloy@redhat.com>, Ying Xue <ying.xue@windriver.com>,
	"David S. Miller" <davem@davemloft.net>, ocfs2-devel@oss.oracle.com
Subject: Re: [Drbd-dev] [PATCH 27/33] sctp: export sctp_setsockopt_bindx
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On Fri, May 15, 2020 at 04:20:02PM +0100, David Howells wrote:
> Christoph Hellwig <hch@lst.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.