Subject: Re: [PATCH 2/3] net: packet: fix information leak to userland

From: Vasiliy Kulikov <[email-masked]>
Date: Sat, 6 Nov 2010 17:39:11 +0300

On Mon, Nov 01, 2010 at 10:14 +0100, walter harms wrote:
> 
> 
> Vasiliy Kulikov schrieb:
> > packet_getname_spkt() doesn't initialize all members of sa_data field of
> > sockaddr struct if strlen(dev->name) < 13.  This structure is then copied
> > to userland.  It leads to leaking of contents of kernel stack memory.
> > We have to fully fill sa_data with strncpy() instead of strlcpy().
> > 
> > The same with packet_getname(): it doesn't initialize sll_pkttype field of
> > sockaddr_ll.  Set it to zero.
> > 
> > Signed-off-by: Vasiliy Kulikov <[email-masked]>
> > ---
> >  net/packet/af_packet.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > index 3616f27..0856a13 100644
> > --- a/net/packet/af_packet.c
> > +++ b/net/packet/af_packet.c
> > @@ -1719,7 +1719,7 @@ static int packet_getname_spkt(struct socket *sock, struct sockaddr *uaddr,
> >  	rcu_read_lock();
> >  	dev = dev_get_by_index_rcu(sock_net(sk), pkt_sk(sk)->ifindex);
> >  	if (dev)
> > -		strlcpy(uaddr->sa_data, dev->name, 15);
> > +		strncpy(uaddr->sa_data, dev->name, 14);
> >  	else
> >  		memset(uaddr->sa_data, 0, 14);
> 
> if i understand the code correcly the max size for dev->name is IFNAMSIZ.

For dev->name - IFNAMSIZ, for uaddr->sa_data - 14.

> You can simply that part:
> 
> memset(uaddr->sa_data, 0, IFNAMSIZ);
> dev = dev_get_by_index_rcu(sock_net(sk), pkt_sk(sk)->ifindex);
> if (dev)
> 	strlcpy(uaddr->sa_data, dev->name, IFNAMSIZ);

This will overflow uaddr->sa_data.  Also I don't see any difficulty to
fill the array only once.

> you should send that as separate patch.
> re,
>  wh
> 
> 
> >  	rcu_read_unlock();
> > @@ -1742,6 +1742,7 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr,
> >  	sll->sll_family = AF_PACKET;
> >  	sll->sll_ifindex = po->ifindex;
> >  	sll->sll_protocol = po->num;
> > +	sll->sll_pkttype = 0;
> >  	rcu_read_lock();
> >  	dev = dev_get_by_index_rcu(sock_net(sk), po->ifindex);
> >  	if (dev) {

Thanks,

-- 
Vasiliy