Currently, GRO can do unlimited recursion through the gro_receive
handlers.  This was fixed for tunneling protocols by limiting tunnel GRO
to one level with encap_mark, but both VLAN and TEB still have this
problem.  Thus, the kernel is vulnerable to a stack overflow, if we
receive a packet composed entirely of VLAN headers.

This patch adds a recursion counter to the GRO layer to prevent stack
overflow.  When a gro_receive function hits the recursion limit, GRO is
aborted for this skb and it is processed normally.

Thanks to Vladim√≠r BeneŇ° <vbe...@redhat.com> for the initial bug report.

Fixes: CVE-2016-7039
Fixes: 9b174d88c257 ("net: Add Transparent Ethernet Bridging GRO support.")
Fixes: 66e5133f19e9 ("vlan: Add GRO support for non hardware accelerated vlan")
Signed-off-by: Sabrina Dubroca <s...@queasysnail.net>
Reviewed-by: Jiri Benc <jb...@redhat.com>
Acked-by: Hannes Frederic Sowa <han...@stressinduktion.org>
---
 drivers/net/geneve.c      |  2 +-
 drivers/net/vxlan.c       |  2 +-
 include/linux/netdevice.h | 24 +++++++++++++++++++++++-
 net/8021q/vlan.c          |  2 +-
 net/core/dev.c            |  1 +
 net/ethernet/eth.c        |  2 +-
 net/ipv4/af_inet.c        |  2 +-
 net/ipv4/fou.c            |  4 ++--
 net/ipv4/gre_offload.c    |  2 +-
 net/ipv4/udp_offload.c    |  8 +++++++-
 net/ipv6/ip6_offload.c    |  2 +-
 11 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 3c20e87bb761..16af1ce99233 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -453,7 +453,7 @@ static struct sk_buff **geneve_gro_receive(struct sock *sk,
 
        skb_gro_pull(skb, gh_len);
        skb_gro_postpull_rcsum(skb, gh, gh_len);
-       pp = ptype->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ptype->callbacks.gro_receive, head, skb);
        flush = 0;
 
 out_unlock:
diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index e7d16687538b..c1639a3e95a4 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -583,7 +583,7 @@ static struct sk_buff **vxlan_gro_receive(struct sock *sk,
                }
        }
 
-       pp = eth_gro_receive(head, skb);
+       pp = call_gro_receive(eth_gro_receive, head, skb);
        flush = 0;
 
 out:
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 136ae6bbe81e..11a7218c3661 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2169,7 +2169,10 @@ struct napi_gro_cb {
        /* Used to determine if flush_id can be ignored */
        u8      is_atomic:1;
 
-       /* 5 bit hole */
+       /* Number of gro_receive callbacks this packet already went through */
+       u8 recursion_counter:4;
+
+       /* 1 bit hole */
 
        /* used to support CHECKSUM_COMPLETE for tunneling protocols */
        __wsum  csum;
@@ -2180,6 +2183,25 @@ struct napi_gro_cb {
 
 #define NAPI_GRO_CB(skb) ((struct napi_gro_cb *)(skb)->cb)
 
+#define GRO_RECURSION_LIMIT 15
+static inline int gro_recursion_inc_test(struct sk_buff *skb)
+{
+       return ++NAPI_GRO_CB(skb)->recursion_counter == GRO_RECURSION_LIMIT;
+}
+
+typedef struct sk_buff **(*gro_receive_t)(struct sk_buff **, struct sk_buff *);
+static inline struct sk_buff **call_gro_receive(gro_receive_t cb,
+                                               struct sk_buff **head,
+                                               struct sk_buff *skb)
+{
+       if (gro_recursion_inc_test(skb)) {
+               NAPI_GRO_CB(skb)->flush |= 1;
+               return NULL;
+       }
+
+       return cb(head, skb);
+}
+
 struct packet_type {
        __be16                  type;   /* This is really htons(ether_type). */
        struct net_device       *dev;   /* NULL is wildcarded here           */
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 8de138d3306b..f2531ad66b68 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -664,7 +664,7 @@ static struct sk_buff **vlan_gro_receive(struct sk_buff 
**head,
 
        skb_gro_pull(skb, sizeof(*vhdr));
        skb_gro_postpull_rcsum(skb, vhdr, sizeof(*vhdr));
-       pp = ptype->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ptype->callbacks.gro_receive, head, skb);
 
 out_unlock:
        rcu_read_unlock();
diff --git a/net/core/dev.c b/net/core/dev.c
index f1fe26f66458..f7cd4b8b035d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4511,6 +4511,7 @@ static enum gro_result dev_gro_receive(struct napi_struct 
*napi, struct sk_buff
                NAPI_GRO_CB(skb)->flush = 0;
                NAPI_GRO_CB(skb)->free = 0;
                NAPI_GRO_CB(skb)->encap_mark = 0;
+               NAPI_GRO_CB(skb)->recursion_counter = 0;
                NAPI_GRO_CB(skb)->is_fou = 0;
                NAPI_GRO_CB(skb)->is_atomic = 1;
                NAPI_GRO_CB(skb)->gro_remcsum_start = 0;
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 66dff5e3d772..02acfff36028 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -439,7 +439,7 @@ struct sk_buff **eth_gro_receive(struct sk_buff **head,
 
        skb_gro_pull(skb, sizeof(*eh));
        skb_gro_postpull_rcsum(skb, eh, sizeof(*eh));
-       pp = ptype->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ptype->callbacks.gro_receive, head, skb);
 
 out_unlock:
        rcu_read_unlock();
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 1effc986739e..9648c97e541f 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1391,7 +1391,7 @@ struct sk_buff **inet_gro_receive(struct sk_buff **head, 
struct sk_buff *skb)
        skb_gro_pull(skb, sizeof(*iph));
        skb_set_transport_header(skb, skb_gro_offset(skb));
 
-       pp = ops->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);
 
 out_unlock:
        rcu_read_unlock();
diff --git a/net/ipv4/fou.c b/net/ipv4/fou.c
index cf50f7e2b012..030d1531e897 100644
--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -249,7 +249,7 @@ static struct sk_buff **fou_gro_receive(struct sock *sk,
        if (!ops || !ops->callbacks.gro_receive)
                goto out_unlock;
 
-       pp = ops->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);
 
 out_unlock:
        rcu_read_unlock();
@@ -441,7 +441,7 @@ static struct sk_buff **gue_gro_receive(struct sock *sk,
        if (WARN_ON_ONCE(!ops || !ops->callbacks.gro_receive))
                goto out_unlock;
 
-       pp = ops->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);
        flush = 0;
 
 out_unlock:
diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index 96e0efecefa6..d5cac99170b1 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -229,7 +229,7 @@ static struct sk_buff **gre_gro_receive(struct sk_buff 
**head,
        /* Adjusted NAPI_GRO_CB(skb)->csum after skb_gro_pull()*/
        skb_gro_postpull_rcsum(skb, greh, grehlen);
 
-       pp = ptype->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ptype->callbacks.gro_receive, head, skb);
        flush = 0;
 
 out_unlock:
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index f9333c963607..7b5879bcd08b 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -295,7 +295,13 @@ struct sk_buff **udp_gro_receive(struct sk_buff **head, 
struct sk_buff *skb,
 
        skb_gro_pull(skb, sizeof(struct udphdr)); /* pull encapsulating udp 
header */
        skb_gro_postpull_rcsum(skb, uh, sizeof(struct udphdr));
-       pp = udp_sk(sk)->gro_receive(sk, head, skb);
+
+       if (gro_recursion_inc_test(skb)) {
+               flush = 1;
+               pp = NULL;
+       } else {
+               pp = udp_sk(sk)->gro_receive(sk, head, skb);
+       }
 
 out_unlock:
        rcu_read_unlock();
diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index e7bfd55899a3..1fcf61f1cbc3 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -246,7 +246,7 @@ static struct sk_buff **ipv6_gro_receive(struct sk_buff 
**head,
 
        skb_gro_postpull_rcsum(skb, iph, nlen);
 
-       pp = ops->callbacks.gro_receive(head, skb);
+       pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);
 
 out_unlock:
        rcu_read_unlock();
-- 
2.10.0

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