[NET]: Fix sk->sk_filter field access

Function sk_filter() is called from tcp_v{4,6}_rcv() functions with arg
needlock = 0, while socket is not locked at that moment. In order to avoid
this and similar issues in the future, use rcu for sk->sk_filter field read
protection.

Signed-off-by: Dmitry Mishin <dim@openvz.org>
Signed-off-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: Kirill Korotaev <dev@openvz.org>

1 files changed, 18 insertions, 25 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 300215bdbf46..f4ccb90e6739 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -427,21 +427,24 @@ out_unlock:
 }
 #endif
 
-static inline unsigned run_filter(struct sk_buff *skb, struct sock *sk, unsigned res)
+static inline int run_filter(struct sk_buff *skb, struct sock *sk,
+                                                        unsigned *snaplen)
 {
         struct sk_filter *filter;
+        int err = 0;
 
-        bh_lock_sock(sk);
-        filter = sk->sk_filter;
-        /*
-         * Our caller already checked that filter != NULL but we need to
-         * verify that under bh_lock_sock() to be safe
-         */
-        if (likely(filter != NULL))
-                res = sk_run_filter(skb, filter->insns, filter->len);
-        bh_unlock_sock(sk);
+        rcu_read_lock_bh();
+        filter = rcu_dereference(sk->sk_filter);
+        if (filter != NULL) {
+                err = sk_run_filter(skb, filter->insns, filter->len);
+                if (!err)
+                        err = -EPERM;
+                else if (*snaplen > err)
+                        *snaplen = err;
+        }
+        rcu_read_unlock_bh();
 
-        return res;
+        return err;
 }
 
 /*
@@ -491,13 +494,8 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev, struct packet
 
         snaplen = skb->len;
 
-        if (sk->sk_filter) {
-                unsigned res = run_filter(skb, sk, snaplen);
-                if (res == 0)
-                        goto drop_n_restore;
-                if (snaplen > res)
-                        snaplen = res;
-        }
+        if (run_filter(skb, sk, &snaplen) < 0)
+                goto drop_n_restore;
 
         if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
             (unsigned)sk->sk_rcvbuf)
@@ -593,13 +591,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
 
         snaplen = skb->len;
 
-        if (sk->sk_filter) {
-                unsigned res = run_filter(skb, sk, snaplen);
-                if (res == 0)
-                        goto drop_n_restore;
-                if (snaplen > res)
-                        snaplen = res;
-        }
+        if (run_filter(skb, sk, &snaplen) < 0)
+                goto drop_n_restore;
 
         if (sk->sk_type == SOCK_DGRAM) {
                 macoff = netoff = TPACKET_ALIGN(TPACKET_HDRLEN) + 16;