linux-kernel - Re: [PATCH v2] Introduce a version6 of autofs interface, to fix design error.

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Date:	Fri, 27 Apr 2012 13:42:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Michael Tokarev <mjt@....msk.ru>,
	Linux-kernel <linux-kernel@...r.kernel.org>,
	autofs@...r.kernel.org, Ian Kent <raven@...maw.net>,
	Thomas Meyer <thomas@...3r.de>, stable@...nel.org
Subject: Re: [PATCH v2] Introduce a version6 of autofs interface, to fix design
 error.

On 04/27/2012 11:19 AM, Linus Torvalds wrote:
> 
> Btw, the whole autofs protocol is *full* of stuff like this. I just
> looked at some other places where the automount daemon does reads of
> fixed sizes, and one of them is a "sizeof(enum states)". Doing a
> sizeof() on an enum is a f*cking bad idea - it's not very well-defined
> at all (different compilers will consider the enum different sizes -
> seriously). But at least that one seems to be something that is purely
> internal to autofs - but it does show that the people involved did not
> think through and design the protocols they used in general - more of
> these kinds of "random sizes of random data structures that we don't
> understand".
> 

The really *really* damning thing with the v5 structure is that it
padded out the whole structure so it wouldn't have to do two read()
operations.  There is a header with a length field in it (which is still
there), and the daemon just ignores it...

	-hpa


P.S. This can still be fixed in user space, by reading the shorter
length, and then eating any additional zeroes.  The kernel does zero out
the extra pad.

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