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!


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