netdev - Re: [patch] Fix handling of overlength pathname in AF_UNIX sun

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Date:	Tue, 17 Apr 2012 11:43:30 -0400
From:	"Carlos O'Donell" <carlos@...temhalted.org>
To:	Willy Tarreau <w@....eu>
Cc:	Michael Kerrisk <mtk.manpages@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-api@...r.kernel.org, yoshfuji@...ux-ipv6.org,
	David Miller <davem@...emloft.net>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [patch] Fix handling of overlength pathname in AF_UNIX sun_path

On Tue, Apr 17, 2012 at 6:51 AM, Willy Tarreau <w@....eu> wrote:
> Hi Michael,
>
> On Tue, Apr 17, 2012 at 10:44:15PM +1200, Michael Kerrisk wrote:
> (...)
>> The accompanying patch changes unix_mkname() to ensure that a terminating
>> null byte is always located within the first 108 bytes of sun_path.
>> It does change the ABI for the former case where a pathname ran to 108
>> bytes without a null terminator: for that case, the call now fails with
>> the error -EINVAL. What are people's thoughts on applying this?
>
> My personal opinion is that (as you said), the risk of breaking existing
> apps is already fairly low, but we must not deliberately break existing
> apps. Eventhough there are currently a log, this is exactly what sysctls
> are made for. I would personally like to have a default limit to 107 chars
> + one zero, with a sysctl option to revert to current behaviour if ever it
> broke an application. In my opinion it's exactly comparable to the risk of
> breaking apps with mmap_min_addr : very low risk but must be covered by a
> workaround (sysctl).

To further the opinion that the risk is low:

The Open Solaris SUN_LEN macro uses strlen to compute the length.

The glibc SUN_LEN macro uses strlen to compute the length.

The Mac OS X libc SUN_LEN macro uses strlen to compute the length.

The linux man-pages project sets the user expectation that it is a
`null-terminated string' (circular argument).

I see every expectation from userspace/glibc that it should be 107 chars + '\0'.

Cheers,
Carlos.
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