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Date:   Thu, 21 May 2020 10:46:33 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christoph Hellwig' <hch@....de>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "Marcelo Ricardo Leitner" <marcelo.leitner@...il.com>,
        Jon Maloy <jmaloy@...hat.com>,
        Ying Xue <ying.xue@...driver.com>,
        "drbd-dev@...ts.linbit.com" <drbd-dev@...ts.linbit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "linux-afs@...ts.infradead.org" <linux-afs@...ts.infradead.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "cluster-devel@...hat.com" <cluster-devel@...hat.com>,
        "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
        "rds-devel@....oracle.com" <rds-devel@....oracle.com>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>
Subject: RE: remove kernel_setsockopt and kernel_getsockopt v2

From: 'Christoph Hellwig'
> Sent: 21 May 2020 10:12
...
> > I worried about whether getsockopt() should read the entire
> > user buffer first. SCTP needs the some of it often (including a
> > sockaddr_storage in one case), TCP needs it once.
> > However the cost of reading a few words is small, and a big
> > buffer probably needs setting to avoid leaking kernel
> > memory if the structure has holes or fields that don't get set.
> > Reading from userspace solves both issues.
> 
> As mention in the thread on the last series:  That was my first idea, but
> we have way to many sockopts, especially in obscure protocols that just
> hard code the size.  The chance of breaking userspace in a way that can't
> be fixed without going back to passing user pointers to get/setsockopt
> is way to high to commit to such a change unfortunately.

Right the syscall stubs probably can't do it.
But the per-protocol ones can for the main protocols.

I posted a patch for SCTP yesterday that removes 800 lines
of source and 8k of object code.
Even that needs a horrid bodge for one request where the
length returned has to be less than the data copied!

	David

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