af_packet: prevent information leak

In 2.6.27, commit 393e52e33c6c2 (packet: deliver VLAN TCI to userspace)
added a small information leak.

Add padding field and make sure its zeroed before copy to user.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/if_packet.h b/include/linux/if_packet.h
index 6d66ce1791a9..7b318630139f 100644
--- a/include/linux/if_packet.h
+++ b/include/linux/if_packet.h
@@ -62,6 +62,7 @@ struct tpacket_auxdata {
         __u16           tp_mac;
         __u16           tp_net;
         __u16           tp_vlan_tci;
+        __u16           tp_padding;
 };
 
 /* Rx ring - header status */
@@ -101,6 +102,7 @@ struct tpacket2_hdr {
         __u32           tp_sec;
         __u32           tp_nsec;
         __u16           tp_vlan_tci;
+        __u16           tp_padding;
 };
 
 #define TPACKET2_HDRLEN         (TPACKET_ALIGN(sizeof(struct tpacket2_hdr)) + sizeof(struct sockaddr_ll))
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index ba248d93399a..c0c3cda19712 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -804,6 +804,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
                 } else {
                         h.h2->tp_vlan_tci = 0;
                 }
+                h.h2->tp_padding = 0;
                 hdrlen = sizeof(*h.h2);
                 break;
         default:
@@ -1736,6 +1737,7 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
                 } else {
                         aux.tp_vlan_tci = 0;
                 }
+                aux.tp_padding = 0;
                 put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(aux), &aux);
         }