netdev - Re: [PATCH] sctp: Fix mangled IPv4 addresses on a IPv6 listening socket

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Date:	Wed, 27 May 2015 10:06:25 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Daniel Borkmann <dborkman@...hat.com>, linux-sctp@...r.kernel.org,
	Vlad Yasevich <vyasevich@...il.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH] sctp: Fix mangled IPv4 addresses on a IPv6 listening
 socket

On Tue, May 26, 2015 at 05:30:17PM -0600, Jason Gunthorpe wrote:
> sctp_v4_map_v6 was subtly writing and reading from members
> of a union in a way the clobbered data it needed to read before
> it read it.
> 
> Zeroing the v6 flowinfo overwrites the v4 sin_addr with 0, meaning
> that every place that calls sctp_v4_map_v6 gets ::ffff:0.0.0.0 as the
> result.
> 
> Reorder things to guarantee correct behaviour no matter what the
> union layout is.
> 
> This impacts user space clients that open an IPv6 SCTP socket and
> receive IPv4 connections. Prior to 299ee user space would see a
> sockaddr with AF_INET and a correct address, after 299ee the sockaddr
> is AF_INET6, but the address is wrong.
> 
> Fixes: 299ee123e198 (sctp: Fixup v4mapped behaviour to comply with Sock API)
> Signed-off-by: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
> ---
>  include/net/sctp/sctp.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> This bugfix should be a candidate for -stable
> 
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index 856f01cb51dd..230775f5952a 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -571,11 +571,14 @@ static inline void sctp_v6_map_v4(union sctp_addr *addr)
>  /* Map v4 address to v4-mapped v6 address */
>  static inline void sctp_v4_map_v6(union sctp_addr *addr)
>  {
> +	__be16 port;
> +
> +	port = addr->v4.sin_port;
> +	addr->v6.sin6_addr.s6_addr32[3] = addr->v4.sin_addr.s_addr;
> +	addr->v6.sin6_port = port;
>  	addr->v6.sin6_family = AF_INET6;
>  	addr->v6.sin6_flowinfo = 0;
>  	addr->v6.sin6_scope_id = 0;
> -	addr->v6.sin6_port = addr->v4.sin_port;
> -	addr->v6.sin6_addr.s6_addr32[3] = addr->v4.sin_addr.s_addr;
>  	addr->v6.sin6_addr.s6_addr32[0] = 0;
>  	addr->v6.sin6_addr.s6_addr32[1] = 0;
>  	addr->v6.sin6_addr.s6_addr32[2] = htonl(0x0000ffff);
> -- 
> 2.1.4
> 
> --
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> 

Nice catch
Acked-by: Neil Horman <nhorman@...driver.com>

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