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 <[email protected]>
Signed-off-by: Hannes Frederic Sowa <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index dcf6ec27739b1d8bfb98c82e8902ca0b697df5f8..278738873703c119dfa322c13b2755e2176a61f5 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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);

diff --git a/include/net/ip.h b/include/net/ip.h
index 025c61c0dffbfe9ddfcc2cd6f9eb38b2af504d3f..6cc1eafb153a75c4665f375836f5592c282f9a8f 100644 (file)
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -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);
 
 /*

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 1d09b46c1e489325b95f9987327d95ca8affed08..eda131d179d971147f5b7ac254876dbf07946861 100644 (file)
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -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));

diff --git a/include/net/sock.h b/include/net/sock.h
index ab186b1d31fffe7cc5b4888d85aca99c2d875da4..e4079c28e6b8588da92a8826d63e07195859a33b 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -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);

diff --git a/net/core/dev.c b/net/core/dev.c
index 962ee9d719641291853715f366717bf1626e115c..45109b70664e8abb1b7957aabd619c4e0d711db4 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -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
 
 /**

diff --git a/net/core/sock.c b/net/core/sock.c
index 78e89eb7eb705624d3ff63324f5002ae10b51145..71e3e5f1eaa04816b8bdd1d34b4fd575f19793b9 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -653,6 +653,25 @@ static inline void sock_valbool_flag(struct sock *sk, int bit, int valbool)
                sock_reset_flag(sk, bit);
 }
 
+bool sk_mc_loop(struct sock *sk)
+{
+       if (dev_recursion_level())
+               return false;
+       if (!sk)
+               return true;
+       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 true;
+}
+EXPORT_SYMBOL(sk_mc_loop);
+
 /*
  *     This is meant for all protocols to use and covers goings on
  *     at the socket level. Everything here is generic.

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 7e80b61b51ff474db6c188218b70f12709209256..36cf0ab685a00d57fbdc6787ba77116dae638f21 100644 (file)
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -542,7 +542,8 @@ int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 {
        struct sk_buff *frag;
        struct rt6_info *rt = (struct rt6_info *)skb_dst(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;
        struct ipv6hdr *tmp_hdr;
        struct frag_hdr *fh;
        unsigned int mtu, hlen, left, len;