Commit 52f1454f authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

packet: allow to transmit +4 byte in TX_RING slot for VLAN case

Commit 57f89bfa ("network: Allow af_packet to transmit +4 bytes
for VLAN packets.") added the possibility for non-mmaped frames to
send extra 4 byte for VLAN header so the MTU increases from 1500 to
1504 byte, for example.

Commit cbd89acb ("af_packet: fix for sending VLAN frames via
packet_mmap") attempted to fix that for the mmap part but was
reverted as it caused regressions while using eth_type_trans()
on output path.

Lets just act analogous to 57f89bfa

 and add a similar logic
to TX_RING. We presume size_max as overcharged with +4 bytes and
later on after skb has been built by tpacket_fill_skb() check
for ETH_P_8021Q header on packets larger than normal MTU. Can
be easily reproduced with a slightly modified trafgen in mmap(2)
mode, test cases:

 { fill(0xff, 12) const16(0x8100) fill(0xff, <1504|1505>) }
 { fill(0xff, 12) const16(0x0806) fill(0xff, <1500|1501>) }

Note that we need to do the test right after tpacket_fill_skb()
as sockets can have PACKET_LOSS set where we would not fail but
instead just continue to traverse the ring.

Reported-by: default avatarMathias Kretschmer <>
Signed-off-by: default avatarDaniel Borkmann <>
Cc: Ben Greear <>
Cc: Phil Sutter <>
Tested-by: default avatarMathias Kretschmer <>
Signed-off-by: default avatarDavid S. Miller <>
parent 07cb1c17
......@@ -2257,8 +2257,7 @@ 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;
reserve = dev->hard_header_len + VLAN_HLEN;
size_max = po->tx_ring.frame_size
- (po->tp_hdrlen - sizeof(struct sockaddr_ll));
......@@ -2285,8 +2284,19 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
goto out_status;
tp_len = tpacket_fill_skb(po, skb, ph, dev, size_max, proto,
addr, hlen);
addr, hlen);
if (tp_len > dev->mtu + dev->hard_header_len) {
struct ethhdr *ehdr;
/* Earlier code assumed this would be a VLAN pkt,
* double-check this now that we have the actual
* packet in hand.
ehdr = eth_hdr(skb);
if (ehdr->h_proto != htons(ETH_P_8021Q))
tp_len = -EMSGSIZE;
if (unlikely(tp_len < 0)) {
if (po->tp_loss) {
__packet_set_status(po, ph,
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