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packet: tpacket_snd(): fix signed/unsigned comparison 

tpacket_fill_skb() can return a negative value (-errno) which
is stored in tp_len variable. In that case the following
condition will be (but shouldn't be) true:

tp_len > dev->mtu + dev->hard_header_len

as dev->mtu and dev->hard_header_len are both unsigned.

That may lead to just returning an incorrect EMSGSIZE errno
to the user.

Fixes: 52f1454f62 ("packet: allow to transmit +4 byte in TX_RING slot for VLAN case")
Signed-off-by: Alexander Drozdov <al.drozdov@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Drozdov 2015-07-28 13:57:01 +03:00 committed by David S. Miller
parent 11c91ef98f
commit dbd46ab412
1 changed files with 2 additions and 1 deletions
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3
net/packet/af_packet.c
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@ -2403,7 +2403,8 @@ 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 (tp_len > dev->mtu + dev->hard_header_len) {
if (likely(tp_len >= 0) &&
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