linux-kernel - Re: [PATCH] unix: properly account for FDs passed over unix sockets

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Message-ID: <20151230112317.GC14049@1wt.eu>
Date:	Wed, 30 Dec 2015 12:23:17 +0100
From:	Willy Tarreau <w@....eu>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Eric Dumazet <edumazet@...gle.com>, socketpair@...il.com
Subject: Re: [PATCH] unix: properly account for FDs passed over unix sockets

On Wed, Dec 30, 2015 at 09:58:42AM +0100, Hannes Frederic Sowa wrote:
> The MSG_PEEK code should not be harmful and the patch is good as is. I 
> first understood from the published private thread, that it is possible 
> for a program to exceed the rlimit of fds. But the DoS is only by 
> keeping the fds in flight and not attaching them to any program.

Exactly. The real issue is when these FDs become very expensive such as
pipes full of data.

> __alloc_fd, called on the receiver side, does check for the rlimit 
> maximum anyway, so I don't see a loophole anymore:
> 
> Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Thanks!

> Another idea would be to add the amount of memory used to manage the fds 
> to sock_rmem/wmem but I don't see any advantages or disadvantages.

Compared to the impact of the pending data in pipes themselves in flight,
this would remain fairly minimal.

Thanks,
Willy

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