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

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Message-Id: <200905221026.51789.remi.denis-courmont@nokia.com>
Date:	Fri, 22 May 2009 10:26:51 +0300
From:	"Rémi Denis-Courmont" 
	<remi.denis-courmont@...ia.com>
To:	ext Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Chris Van Hoof <vanhoof@...hat.com>,
	Clark Williams <williams@...hat.com>
Subject: Re: [RFC 2/2] net: Allow protocols to provide an unlocked_recvmsg sk_prot method

On Thursday 21 May 2009 02:06:59 ext Arnaldo Carvalho de Melo wrote:
> So that the socket layer kwows which protocol uses locking and can ask
> for an unlocked recvmsg call inside recvmmsg, that takes the lock for a
> batch of packets.
>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  include/linux/socket.h |    3 ++
>  include/net/sock.h     |    5 ++++
>  net/core/sock.c        |   11 +++++++--
>  net/ipv4/udp.c         |   52
> ++++++++++++++++++++++++++++++++++++++++------- net/socket.c           |  
> 39 ++++++++++++++++++++++++----------- 5 files changed, 87 insertions(+),
> 23 deletions(-)
>
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index 50c6c44..7ef30a3 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -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?

-- 
Rémi Denis-Courmont
Nokia Devices R&D, Maemo Software, Helsinki

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