netdev - Re: [PATCH] UNIX: Do not loop forever at unix

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Message-ID: <1283370450.2484.19.camel@edumazet-laptop>
Date:	Wed, 01 Sep 2010 21:47:30 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] UNIX: Do not loop forever at unix_autobind().

Le lundi 30 août 2010 à 22:27 +0900, Tetsuo Handa a écrit :
> I tried to create and autobind 1048576 UNIX domain sockets using
> http://I-love.SAKURA.ne.jp/tmp/unixloop.asm on 2.6.18-194.11.1.el5.x86_64,
> and found that it needs about 2GB of RAM. Thus, on systems where
> /proc/sys/fs/file-max is larger than 1048576, a local user can create and
> autobind 1048576 UNIX domain sockets in order to let applications fall into
> 
>   while (1)
>   	yield();
> 
> loop. Below is the patch (only compile tested) to avoid falling into this loop.
> Is there any reason a name has to be '\0' + 5 letters?
> Shoud I give up after checking 1048576 names rather than after checking
> 4294967296 names?

Yes please. Fix the bug first.

Then, a following patch to increase current limit, if necessary.

> ----------------------------------------

>  
>  	err = -ENOMEM;
> -	addr = kzalloc(sizeof(*addr) + sizeof(short) + 16, GFP_KERNEL);
> +	addr = kzalloc(sizeof(*addr) + sizeof(short) + 19, GFP_KERNEL);

IMHO, this 16 or 19 value is wrong, we need less memory than that.

(But this will be adressed in a 2nd patch)

Thanks


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