linux-kernel - Re: RFC: disablenetwork facility. (v4)

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Message-ID: <20091227085113.GX18217@ZenIV.linux.org.uk>
Date:	Sun, 27 Dec 2009 08:51:13 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	michael@...top.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-security-module@...r.kernel.org,
	andi@...stfloor.org, david@...g.hm, socketcan@...tkopp.net,
	alan@...rguk.ukuu.org.uk, herbert@...dor.apana.org.au,
	Valdis.Kletnieks@...edu, bdonlan@...il.com, zbr@...emap.net,
	cscott@...ott.net, jmorris@...ei.org, ebiederm@...ssion.com,
	bernie@...ewiz.org, mrs@...hic-beasts.com, randy.dunlap@...cle.com,
	xiyou.wangcong@...il.com, sam@...ack.fr, casey@...aufler-ca.com,
	serue@...ibm.com, pavel@....cz
Subject: Re: RFC: disablenetwork facility. (v4)

On Sun, Dec 27, 2009 at 05:36:48PM +0900, Tetsuo Handa wrote:

> Application writers know better what syscalls the application will call than
> application users.

Aren't you forgetting about libc?  Seriously, any interface along the
lines of "pass a set of syscall numbers to kernel" is DOA:
	* syscall numbers are architecture-dependent
	* there are socketcall-style multiplexors (sys_ipc, anyone?)
	* libc is free to substitute one for another
	* libc is free to do so in arch-specific manner
	* libc is free to do so in kernel-revision-specific manner
	* libc is free to do so in libc-revision-specific manner
(... and does all of the above)
	* new syscalls get added
	* e.g. on sparc64 32bit task can issue 64bit syscalls
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