netdev - Re: [PATCH] Use unsigned variables for packet lengths in ip[6]

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Date:	Thu, 02 Jun 2011 13:57:42 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	davej@...hat.com
Cc:	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	pablo@...filter.org, kaber@...sh.net
Subject: Re: [PATCH] Use unsigned variables for packet lengths in
 ip[6]_queue.

From: Dave Jones <davej@...hat.com>
Date: Fri, 27 May 2011 20:36:51 -0400

> On Tue, Apr 19, 2011 at 08:41:05PM -0700, David Miller wrote:
>  > From: Dave Jones <davej@...hat.com>
>  > Date: Tue, 19 Apr 2011 21:42:22 -0400
>  > 
>  > > Not catastrophic, but ipqueue seems to be too trusting of what it gets
>  > > passed from userspace, and passes it on down to the page allocator,
>  > > where it will spew warnings if the page order is too high.
>  > > 
>  > > __ipq_rcv_skb has several checks for lengths too small, but doesn't
>  > > seem to have any for oversized ones.   I'm not sure what the maximum
>  > > we should check for is. I'll code up a diff if anyone has any ideas
>  > > on a sane maximum.
>  > 
>  > Maybe the thing to do is to simply pass __GFP_NOWARN to nlmsg_new()
>  > in netlink_ack()?
>  > 
>  > Anyone else have a better idea?
> 
> So I went back to this today, and found something that doesn't look right.
> After adding some instrumentation, and re-running my tests, I found that
> the reason we were blowing up with enormous allocations was that we
> were passing down a nlmsglen's like -1061109568
> 
> Is there any reason for that to be signed ?
> The nlmsg_len entry of nlmsghdr is a u32, so I'm assuming this is a bug.
> 
> With the patch below, I haven't been able to reproduce the problem, but
> I don't know if I've inadvertantly broken some other behaviour somewhere
> deeper in netlink where this is valid.

netfilter-devel and maintainers CC:'d

> -- 
> 
> Netlink message lengths can't be negative, so use unsigned variables.
> 
> Signed-off-by: Dave Jones <davej@...hat.com>
> 
> diff --git a/net/ipv4/netfilter/ip_queue.c b/net/ipv4/netfilter/ip_queue.c
> index d2c1311..f7f9bd7 100644
> --- a/net/ipv4/netfilter/ip_queue.c
> +++ b/net/ipv4/netfilter/ip_queue.c
> @@ -402,7 +402,8 @@ ipq_dev_drop(int ifindex)
>  static inline void
>  __ipq_rcv_skb(struct sk_buff *skb)
>  {
> -	int status, type, pid, flags, nlmsglen, skblen;
> +	int status, type, pid, flags;
> +	unsigned int nlmsglen, skblen;
>  	struct nlmsghdr *nlh;
>  
>  	skblen = skb->len;
> diff --git a/net/ipv6/netfilter/ip6_queue.c b/net/ipv6/netfilter/ip6_queue.c
> index 413ab07..065fe40 100644
> --- a/net/ipv6/netfilter/ip6_queue.c
> +++ b/net/ipv6/netfilter/ip6_queue.c
> @@ -403,7 +403,8 @@ ipq_dev_drop(int ifindex)
>  static inline void
>  __ipq_rcv_skb(struct sk_buff *skb)
>  {
> -	int status, type, pid, flags, nlmsglen, skblen;
> +	int status, type, pid, flags;
> +	unsigned int nlmsglen, skblen;
>  	struct nlmsghdr *nlh;
>  
>  	skblen = skb->len;
--
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