packet: fix tpacket_snd max frame len

Since it's introduction in commit 69e3c75f4d54 ("net: TX_RING and
packet mmap"), TX_RING could be used from SOCK_DGRAM and SOCK_RAW
side. When used with SOCK_DGRAM only, the size_max > dev->mtu +
reserve check should have reserve as 0, but currently, this is
unconditionally set (in it's original form as dev->hard_header_len).

I think this is not correct since tpacket_fill_skb() would then
take dev->mtu and dev->hard_header_len into account for SOCK_DGRAM,
the extra VLAN_HLEN could be possible in both cases. Presumably, the
reserve code was copied from packet_snd(), but later on missed the
check. Make it similar as we have it in packet_snd().

Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 4 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 0066da2b8e44..242bce1cf0f3 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2510,12 +2510,13 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
         if (unlikely(!(dev->flags & IFF_UP)))
                 goto out_put;
 
-        reserve = dev->hard_header_len + VLAN_HLEN;
+        if (po->sk.sk_socket->type == SOCK_RAW)
+                reserve = dev->hard_header_len;
         size_max = po->tx_ring.frame_size
                 - (po->tp_hdrlen - sizeof(struct sockaddr_ll));
 
-        if (size_max > dev->mtu + reserve)
-                size_max = dev->mtu + reserve;
+        if (size_max > dev->mtu + reserve + VLAN_HLEN)
+                size_max = dev->mtu + reserve + VLAN_HLEN;
 
         do {
                 ph = packet_current_frame(po, &po->tx_ring,
@@ -2542,7 +2543,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
                 tp_len = tpacket_fill_skb(po, skb, ph, dev, size_max, proto,
                                           addr, hlen);
                 if (likely(tp_len >= 0) &&
-                    tp_len > dev->mtu + dev->hard_header_len &&
+                    tp_len > dev->mtu + reserve &&
                     !packet_extra_vlan_len_allowed(dev, skb))
                         tp_len = -EMSGSIZE;