[PATCH 5/6] netfilter: arp_tables: fix infoleak to userspace CVE-2011-1170

[Stefan Bader]

On 04.07.2011 16:08, paolo.pisati at canonical.com wrote:
> From: Vasiliy Kulikov <segoon at openwall.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/801480
> 
> commit upstream 42eab94fff18cb1091d3501cd284d6bd6cc9c143
> 
> Structures ipt_replace, compat_ipt_replace, and xt_get_revision are
> copied from userspace.  Fields of these structs that are
> zero-terminated strings are not checked.  When they are used as argument
> to a format string containing "%s" in request_module(), some sensitive
> information is leaked to userspace via argument of spawned modprobe
> process.
> 
> The first bug was introduced before the git epoch;  the second is
> introduced by 6b7d31fc (v2.6.15-rc1);  the third is introduced by
> 6b7d31fc (v2.6.15-rc1).  To trigger the bug one should have
> CAP_NET_ADMIN.
> 
> Signed-off-by: Vasiliy Kulikov <segoon at openwall.com>
> Signed-off-by: Patrick McHardy <kaber at trash.net>
> Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
> ---
>  net/ipv4/netfilter/arp_tables.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
> index 2909c92..da85e92 100644
> --- a/net/ipv4/netfilter/arp_tables.c
> +++ b/net/ipv4/netfilter/arp_tables.c
> @@ -816,6 +816,7 @@ static int do_replace(void __user *user, unsigned int len)
>  		return -ENOMEM;
>  	if (tmp.num_counters >= INT_MAX / sizeof(struct xt_counters))
>  		return -ENOMEM;
> +	tmp.name[sizeof(tmp.name)-1] = 0;
>  
>  	newinfo = xt_alloc_table_info(tmp.size);
>  	if (!newinfo)

Comparing the second hunk against upstream there may be a misplacement. In
upstream code the change was in compat_do_replace().

> @@ -930,6 +931,7 @@ static int do_add_counters(void __user *user, unsigned int len)
>  	paddc = vmalloc(len);
>  	if (!paddc)
>  		return -ENOMEM;
> +	tmp.name[sizeof(tmp.name)-1] = 0;
>  
>  	if (copy_from_user(paddc, user, len) != 0) {
>  		ret = -EFAULT;

> @@ -1070,6 +1072,7 @@ static int do_arpt_get_ctl(struct sock *sk, int cmd, void __user *user, int *len
>  			ret = -EFAULT;
>  			break;
>  		}
> +		rev.name[sizeof(rev.name)-1] = 0;
>  
>  		try_then_request_module(xt_find_revision(NF_ARP, rev.name,
>  							 rev.revision, 1, &ret),