netdev - Re: [PATCH] net: Fix security_socket

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Message-Id: <201107231939.FIF21882.QHOSOFtMFVLFOJ@I-love.SAKURA.ne.jp>
Date:	Sat, 23 Jul 2011 19:39:40 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mjt@....msk.ru
Cc:	davem@...emloft.net, casey@...aufler-ca.com, anton@...ba.org,
	netdev@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] net: Fix security_socket_sendmsg() bypass problem.

Michael Tokarev wrote:
> (I noticed samba.org address in the Cc list).

That's because Anton Blanchard is author of sendmmsg() system call.

> When I saw recvmmsg()/sendmmsg() here, my first thought was an
> authoritative DNS server which can read several requests at a
> time and answer them all at once too - this way it all will go
> to different addresses.

I don't know what application wants sendmmsg(). Since users can send up to
UIO_MAXIOV (= 1024) "struct iovec" blocks using sendmsg(), they will use
sendmsg() rather than sendmmsg() if the destination address are the same.

Therefore, I guess users will use sendmmsg() for sending to multiple different
destination addresses. If so, optimization based on destination address will do
more harm than benefit; simply passing nosec flag down to LSM modules (so that
SELinux will skip sock_has_perm() call and SMACK will not skip
smack_netlabel_send() call) will be sufficient for 3.0.x stable release.

Anton, how do you want to use sendmmsg()?
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