tcp: fix SCM_TIMESTAMPING_OPT_STATS for normal skbs

__sock_recv_timestamp can be called for both normal skbs (for
receive timestamps) and for skbs on the error queue (for transmit
timestamps).

Commit 1c885808e456
(tcp: SOF_TIMESTAMPING_OPT_STATS option for SO_TIMESTAMPING)
assumes any skb passed to __sock_recv_timestamp are from
the error queue, containing OPT_STATS in the content of the skb.
This results in accessing invalid memory or generating junk
data.

To fix this, set skb->pkt_type to PACKET_OUTGOING for packets
on the error queue. This is safe because on the receive path
on local sockets skb->pkt_type is never set to PACKET_OUTGOING.
With that, copy OPT_STATS from a packet, only if its pkt_type
is PACKET_OUTGOING.

Fixes: 1c885808e456 ("tcp: SOF_TIMESTAMPING_OPT_STATS option for SO_TIMESTAMPING")
Reported-by: JongHwan Kim <zzoru007@gmail.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index cd4ba8c..b1fbd19 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3694,6 +3694,15 @@ static void sock_rmem_free(struct sk_buff *skb)
        atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
 }
 
+static void skb_set_err_queue(struct sk_buff *skb)
+{
+       /* pkt_type of skbs received on local sockets is never PACKET_OUTGOING.
+        * So, it is safe to (mis)use it to mark skbs on the error queue.
+        */
+       skb->pkt_type = PACKET_OUTGOING;
+       BUILD_BUG_ON(PACKET_OUTGOING == 0);
+}
+
 /*
  * Note: We dont mem charge error packets (no sk_forward_alloc changes)
  */
@@ -3707,6 +3716,7 @@ int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
        skb->sk = sk;
        skb->destructor = sock_rmem_free;
        atomic_add(skb->truesize, &sk->sk_rmem_alloc);
+       skb_set_err_queue(skb);
 
        /* before exiting rcu section, make sure dst is refcounted */
        skb_dst_force(skb);

diff --git a/net/socket.c b/net/socket.c
index e034fe4..692d698 100644 (file)
--- a/net/socket.c
+++ b/net/socket.c
@@ -652,6 +652,16 @@ int kernel_sendmsg(struct socket *sock, struct msghdr *msg,
 }
 EXPORT_SYMBOL(kernel_sendmsg);
 
+static bool skb_is_err_queue(const struct sk_buff *skb)
+{
+       /* pkt_type of skbs enqueued on the error queue are set to
+        * PACKET_OUTGOING in skb_set_err_queue(). This is only safe to do
+        * in recvmsg, since skbs received on a local socket will never
+        * have a pkt_type of PACKET_OUTGOING.
+        */
+       return skb->pkt_type == PACKET_OUTGOING;
+}
+
 /*
  * called from sock_recv_timestamp() if sock_flag(sk, SOCK_RCVTSTAMP)
  */
@@ -695,7 +705,8 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
                put_cmsg(msg, SOL_SOCKET,
                         SCM_TIMESTAMPING, sizeof(tss), &tss);
 
-               if (skb->len && (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_STATS))
+               if (skb_is_err_queue(skb) && skb->len &&
+                   (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_STATS))
                        put_cmsg(msg, SOL_SOCKET, SCM_TIMESTAMPING_OPT_STATS,
                                 skb->len, skb->data);
        }