[3.16.y-ckt stable] Patch "packet: fix tpacket_snd max frame len" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    packet: fix tpacket_snd max frame len

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From f9bdfe5a55a005bf449f6539333535067d12576d Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <daniel at iogearbox.net>
Date: Wed, 11 Nov 2015 23:25:44 +0100
Subject: packet: fix tpacket_snd max frame len

commit 5cfb4c8d05b4409c4044cb9c05b19705c1d9818b upstream.

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 at iogearbox.net>
Acked-by: Willem de Bruijn <willemb at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/packet/af_packet.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 92bb65796fb4..ede33f60991a 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2263,12 +2263,13 @@ 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,
@@ -2292,7 +2293,7 @@ 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;