Bad behaviour when unintentionally mixing ipv4 and ipv6 addresses

Hi,

By chance Reinhard Max spotted an interesting flaw in Linux bind(2)...

If you create a IPv4 socket and then incorrectly bind(2) to a IPv6 address
(which you got from getaddrinfo(3) or similar), the socket will be bound
to INADDR_ANY.

The reason is that the kernel just takes the sockaddr_in6 struct and
evaluates it as a sockaddr_in struct, with the port being OK, but the IPv4
sin_addr overlaying the IPv6 sin6_flowinfo field.

As the sin6_flowinfo field is usually 0, your service can end up listening
to the world.

A testprogram that you can strace is attached, run netstat -apn |grep 12345
afterwards to see it binds 0.0.0.0:12345.

Perhaps add a check like the one below? (untested)
Or use if (addr->sin_family == AF_INET6) to just catch the IPv6 case?

Ciao, Marcus


Subject: [PATCH] net/ipv4: Check for mistakenly passed in non-IPv4 address

Hi,

Check against mistakenly passing in IPv6 addresses (which would result
in an INADDR_ANY bind) or similar incompatible sockaddrs.

Ciao, Marcus

Signed-off-by: Marcus Meissner <meissner@suse.de>
Cc: Reinhard Max <max@suse.de>
---
 net/ipv4/af_inet.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

From: Marcus Meissner <meissner@suse.de>
Date: Wed, 25 May 2011 17:59:18 +0200

> @@ -465,6 +465,9 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
>  	if (addr_len < sizeof(struct sockaddr_in))
>  		goto out;
>  
> +	if (addr->sin_family != AF_INET)
> +		goto out;
> +
>  	chk_addr_ret = inet_addr_type(sock_net(sk), addr->sin_addr.s_addr);

Since we haven't been validating the sin_family field for 18+ years, the
chance to break some applications is very real.

But I think it's more important to fix this (and force any broken apps
to set sin_family correctly).  So I will apply this, thanks.
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On Wed, 1 Jun 2011 at 21:03, David Miller wrote:

> Since we haven't been validating the sin_family field for 18+ years, 
> the chance to break some applications is very real.
>
> But I think it's more important to fix this (and force any broken 
> apps to set sin_family correctly).  So I will apply this, thanks.

I think a corresponding check should also go into inet6_bind() in 
net/ipv6/af_inet6.c .


cu
 	Reinhard
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