netdev - Re: [PATCH net] ipv4: Avoid crashing in ip

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Date:	Sat, 23 May 2015 12:20:05 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	"Vittorio G (VittGam)" <linuxbugs@...tgam.net>,
	security@...nel.org, Greg KH <greg@...ah.com>, luto@...capital.net,
	Willy Tarreau <w@....eu>
Subject: Re: [PATCH net] ipv4: Avoid crashing in ip_error


	Hello,

On Fri, 22 May 2015, Eric W. Biederman wrote:

> ip_error does not check if in_dev is NULL before dereferencing it.
> 
> IThe following sequence of calls is possible:
> CPU A                          CPU B
> ip_rcv_finish
>     ip_route_input_noref()
>         ip_route_input_slow()
>                                inetdev_destroy()
>     dst_input()
> 
> With the result that a network device can be destroyed while processing
> an input packet.

	How can that happen in practice? May be network
driver is missing a napi_disable() call in ndo_stop()?
napi_disable is supposed to wait backlog before NETDEV_DOWN
and NETDEV_UNREGISTER (where inetdev_destroy is called) handlers
are notified. Any link to original crash report, info for used
driver, etc?

	After commit 8030f54499925d ("[IPV4] devinet: Register inetdev 
earlier.") dev->ip_ptr is always present while packets are
processed, only in_dev->ifa_list can be NULL.

Regards

--
Julian Anastasov <ja@....bg>
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