netlink: not trim skb for mmaped socket when dump

We should not trim skb for mmaped socket since its buf size is fixed
and userspace will read as frame which data equals head. mmaped
socket will not call recvmsg, means max_recvmsg_len is 0,
skb_reserve was not called before commit: db65a3aaf29e.

Fixes: db65a3aaf29e (netlink: Trim skb to alloc size to avoid MSG_TRUNC)
Signed-off-by: Ken-ichirou MATSUZAWA <chamas@h4.dion.ne.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 81dc1bb6e0168ed17cd2d60e6dc3a394f0f34e76..f1ffb34e253f4906275d4da99ce26306b94241eb 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2831,7 +2831,8 @@ static int netlink_dump(struct sock *sk)
         * reasonable static buffer based on the expected largest dump of a
         * single netdev. The outcome is MSG_TRUNC error.
         */
-       skb_reserve(skb, skb_tailroom(skb) - alloc_size);
+       if (!netlink_rx_is_mmaped(sk))
+               skb_reserve(skb, skb_tailroom(skb) - alloc_size);
        netlink_skb_set_owner_r(skb, sk);
 
        len = cb->dump(skb, cb);