netdev - Re: [RFC 2/2] net: Allow protocols to provide an unlocked_recvmsg sk

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Date:	Fri, 22 May 2009 11:52:15 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	remi.denis-courmont@...ia.com, netdev@...r.kernel.org,
	vanhoof@...hat.com, williams@...hat.com
Subject: Re: [RFC 2/2] net: Allow protocols to provide an unlocked_recvmsg
	sk_prot method

Em Fri, May 22, 2009 at 12:47:38AM -0700, David Miller escreveu:
> From: "Rémi Denis-Courmont" <remi.denis-courmont@...ia.com>
> Date: Fri, 22 May 2009 10:26:51 +0300
> 
> > On Thursday 21 May 2009 02:06:59 ext Arnaldo Carvalho de Melo wrote:
> >> @@ -265,6 +265,9 @@ struct ucred {
> >>  #define MSG_ERRQUEUE	0x2000	/* Fetch message from error queue */
> >>  #define MSG_NOSIGNAL	0x4000	/* Do not generate SIGPIPE */
> >>  #define MSG_MORE	0x8000	/* Sender will send more */
> >> +#ifdef __KERNEL__
> >> +#define MSG_UNLOCKED	0x10000	/* Don't lock the sock */
> >> +#endif
> > 
> > I might be missing something but... What prevents an evil userland from 
> > setting the flag anyway and hitting the BUG case?
> 
> Yes, we'll need to clear this on all paths where we get msg
> flags from the user.
> 
> There's a lot of such places.
> 
> So maybe we need to pass this state around in a different,
> internal, way.

Yeah, I'll think about it, that was the easiest way to implement it for
the proof of concept we have now. Filtering it out at syscall entry and
at sock_common_recvmsg would fix it, but I'm not sure if its the best
option.

The comments about the interface provided to userspace (struct mmsghdr),
how to return errors after some datagrams were put in the array
(sk->sk_err being stored then returned in the next call), timeouts, etc
are great, thanks, after some more comments I'll respin these patches.

- Arnaldo
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