netdev - Re: [PATCH][NEIGH]: Fix race between pneigh deletion and ipv6's ndisc_recv

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Date:	Mon, 24 Mar 2008 14:50:10 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	xemul@...nvz.org
Cc:	yoshfuji@...ux-ipv6.org, dlezcano@...ibm.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH][NEIGH]: Fix race between pneigh deletion and ipv6's
 ndisc_recv_ns (v3).

From: Pavel Emelyanov <xemul@...nvz.org>
Date: Mon, 24 Mar 2008 11:24:05 +0300

> Proxy neighbors do not have any reference counting, so any caller
> of pneigh_lookup (unless it's a netlink triggered add/del routine)
> should _not_ perform any actions on the found proxy entry. 
> 
> There's one exception from this rule - the ipv6's ndisc_recv_ns() 
> uses found entry to check the flags for NTF_ROUTER.
> 
> This creates a race between the ndisc and pneigh_delete - after 
> the pneigh is returned to the caller, the nd_tbl.lock is dropped 
> and the deleting procedure may proceed.
> 
> One of the fixes would be to add a reference counting, but this
> problem exists for ndisc only. Besides such a patch would be too 
> big for -rc4.
> 
> So I propose to introduce a __pneigh_lookup() which is supposed
> to be called with the lock held and use it in ndisc code to check
> the flags on alive pneigh entry.
> 
> 
> Changes from v2:
> As David noticed, Exported the __pneigh_lookup() to ipv6 module. 
> The checkpatch generates a warning on it, since the EXPORT_SYMBOL 
> does not follow the symbol itself, but in this file all the 
> exports come at the end, so I decided no to break this harmony.
> 
> Changes from v1:
> Fixed comments from YOSHIFUJI - indentation of prototype in header
> and the pndisc_check_router() name - and a compilation fix, pointed
> by Daniel - the is_routed was (falsely) considered as uninitialized
> by gcc.
> 
> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>

Applied, thanks!
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