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Commit f60e5990 authored by hannes@stressinduktion.org's avatar hannes@stressinduktion.org Committed by David S. Miller
Browse files

ipv6: protect skb->sk accesses from recursive dereference inside the stack 



We should not consult skb->sk for output decisions in xmit recursion
levels > 0 in the stack. Otherwise local socket settings could influence
the result of e.g. tunnel encapsulation process.

ipv6 does not conform with this in three places:

1) ip6_fragment: we do consult ipv6_npinfo for frag_size

2) sk_mc_loop in ipv6 uses skb->sk and checks if we should
   loop the packet back to the local socket

3) ip6_skb_dst_mtu could query the settings from the user socket and
   force a wrong MTU

Furthermore:
In sk_mc_loop we could potentially land in WARN_ON(1) if we use a
PF_PACKET socket ontop of an IPv6-backed vxlan device.

Reuse xmit_recursion as we are currently only interested in protecting
tunnel devices.

Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 576b7cd2

include/linux/netdevice.h

+6 −0
Original line number Diff line number Diff line
@@ -2185,6 +2185,12 @@ void netdev_freemem(struct net_device *dev); 
void synchronize_net(void);

int init_dummy_netdev(struct net_device *dev);



DECLARE_PER_CPU(int, xmit_recursion);

static inline int dev_recursion_level(void)

{

	return this_cpu_read(xmit_recursion);

}



struct net_device *dev_get_by_index(struct net *net, int ifindex);

struct net_device *__dev_get_by_index(struct net *net, int ifindex);

struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex);

include/net/ip.h

+0 −16
Original line number Diff line number Diff line
@@ -453,22 +453,6 @@ static __inline__ void inet_reset_saddr(struct sock *sk) 


#endif



static inline int sk_mc_loop(struct sock *sk)

{

	if (!sk)

		return 1;

	switch (sk->sk_family) {

	case AF_INET:

		return inet_sk(sk)->mc_loop;

#if IS_ENABLED(CONFIG_IPV6)

	case AF_INET6:

		return inet6_sk(sk)->mc_loop;

#endif

	}

	WARN_ON(1);

	return 1;

}



bool ip_call_ra_chain(struct sk_buff *skb);



/*

include/net/ip6_route.h

+2 −1
Original line number Diff line number Diff line
@@ -174,7 +174,8 @@ int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *)); 


static inline int ip6_skb_dst_mtu(struct sk_buff *skb)

{

	struct ipv6_pinfo *np = skb->sk ? inet6_sk(skb->sk) : NULL;

	struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?

				inet6_sk(skb->sk) : NULL;



	return (np && np->pmtudisc >= IPV6_PMTUDISC_PROBE) ?

	       skb_dst(skb)->dev->mtu : dst_mtu(skb_dst(skb));

include/net/sock.h

+2 −0
Original line number Diff line number Diff line
@@ -1762,6 +1762,8 @@ struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie); 


struct dst_entry *sk_dst_check(struct sock *sk, u32 cookie);



bool sk_mc_loop(struct sock *sk);



static inline bool sk_can_gso(const struct sock *sk)

{

	return net_gso_ok(sk->sk_route_caps, sk->sk_gso_type);

net/core/dev.c

+3 −1
Original line number Diff line number Diff line
@@ -2848,7 +2848,9 @@ static void skb_update_prio(struct sk_buff *skb) 
#define skb_update_prio(skb)

#endif



static DEFINE_PER_CPU(int, xmit_recursion);

DEFINE_PER_CPU(int, xmit_recursion);

EXPORT_SYMBOL(xmit_recursion);



#define RECURSION_LIMIT 10



/**