Re: [PATCH] net: ipmr/ip6mr: prevent out-of-bounds vif_table access

[Nicolas Dichtel <nicolas.dichtel@dev.6wind.com>]

yes, but I think that it is not enough, ip[6]mr_mfc_add() is only called via 
setsockopt().

When a multicast packet arrived in ip6_mr_input(), if there is no cache 
ip6mr_cache_unresolved() will be called and this function will add an entry with 
parent == 65535.

And the second problem is that when a vif is removed, no cleanup is made in 
cache entry. Hence, we can have a cache entry which points to an invalid vif 
(dev is set ot NULL).


Regards,
Nicolas

Le 26.03.2010 17:51, David Miller a écrit :
> From: Nicolas Dichtel <nicolas.dichtel@dev.6wind.com>
> Date: Fri, 26 Mar 2010 10:45:35 +0100
> 
>> please consider the attached patch about IPv4 and IPv6 multicast.
> 
> Already fixed by Patrick McHardy recently:
> 
> commit a50436f2cd6e85794f7e1aad795ca8302177b896
> Author: Patrick McHardy <kaber@trash.net>
> Date:   Wed Mar 17 06:04:14 2010 +0000
> 
>     net: ipmr/ip6mr: fix potential out-of-bounds vif_table access
>     
>     mfc_parent of cache entries is used to index into the vif_table and is
>     initialised from mfcctl->mfcc_parent. This can take values of to 2^16-1,
>     while the vif_table has only MAXVIFS (32) entries. The same problem
>     affects ip6mr.
>     
>     Refuse invalid values to fix a potential out-of-bounds access. Unlike
>     the other validity checks, this is checked in ipmr_mfc_add() instead of
>     the setsockopt handler since its unused in the delete path and might be
>     uninitialized.
>     
>     Signed-off-by: Patrick McHardy <kaber@trash.net>
>     Signed-off-by: David S. Miller <davem@davemloft.net>
> 
> diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> index 8582e12..0b9d03c 100644
> --- a/net/ipv4/ipmr.c
> +++ b/net/ipv4/ipmr.c
> @@ -802,6 +802,9 @@ static int ipmr_mfc_add(struct net *net, struct mfcctl *mfc, int mrtsock)
>  	int line;
>  	struct mfc_cache *uc, *c, **cp;
>  
> +	if (mfc->mfcc_parent >= MAXVIFS)
> +		return -ENFILE;
> +
>  	line = MFC_HASH(mfc->mfcc_mcastgrp.s_addr, mfc->mfcc_origin.s_addr);
>  
>  	for (cp = &net->ipv4.mfc_cache_array[line];
> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> index 52e0f74..23e4ac0 100644
> --- a/net/ipv6/ip6mr.c
> +++ b/net/ipv6/ip6mr.c
> @@ -1113,6 +1113,9 @@ static int ip6mr_mfc_add(struct net *net, struct mf6cctl *mfc, int mrtsock)
>  	unsigned char ttls[MAXMIFS];
>  	int i;
>  
> +	if (mfc->mf6cc_parent >= MAXMIFS)
> +		return -ENFILE;
> +
>  	memset(ttls, 255, MAXMIFS);
>  	for (i = 0; i < MAXMIFS; i++) {
>  		if (IF_ISSET(i, &mfc->mf6cc_ifset))