[PACKET]: Fix skb->cb clobbering between aux and sockaddr

Both aux data and sockaddr tries to use the same buffer which
obviously doesn't work.  We just happen to have 4 bytes free in
the skb->cb if you take away the maximum length of sockaddr_ll.
That's just enough to store the one piece of info from aux data
that we can't generate at recvmsg(2) time.

This is what the following patch does.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 8973ea7..a6fa487 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -60,6 +60,7 @@
 #include <linux/netdevice.h>
 #include <linux/if_packet.h>
 #include <linux/wireless.h>
+#include <linux/kernel.h>
 #include <linux/kmod.h>
 #include <net/ip.h>
 #include <net/protocol.h>
@@ -215,7 +216,15 @@ struct packet_sock {
 #endif
 };
 
-#define PACKET_SKB_CB(__skb)   ((struct tpacket_auxdata *)((__skb)->cb))
+struct packet_skb_cb {
+       unsigned int origlen;
+       union {
+               struct sockaddr_pkt pkt;
+               struct sockaddr_ll ll;
+       } sa;
+};
+
+#define PACKET_SKB_CB(__skb)   ((struct packet_skb_cb *)((__skb)->cb))
 
 #ifdef CONFIG_PACKET_MMAP
 
@@ -296,7 +305,7 @@ static int packet_rcv_spkt(struct sk_buff *skb, struct net_device *dev,  struct
        /* drop conntrack reference */
        nf_reset(skb);
 
-       spkt = (struct sockaddr_pkt*)skb->cb;
+       spkt = &PACKET_SKB_CB(skb)->sa.pkt;
 
        skb_push(skb, skb->data-skb->mac.raw);
 
@@ -465,7 +474,6 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev, struct packet
        u8 * skb_head = skb->data;
        int skb_len = skb->len;
        unsigned int snaplen, res;
-       struct tpacket_auxdata *aux;
 
        if (skb->pkt_type == PACKET_LOOPBACK)
                goto drop;
@@ -516,7 +524,10 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev, struct packet
                skb = nskb;
        }
 
-       sll = (struct sockaddr_ll*)skb->cb;
+       BUILD_BUG_ON(sizeof(*PACKET_SKB_CB(skb)) + MAX_ADDR_LEN - 8 >
+                    sizeof(skb->cb));
+
+       sll = &PACKET_SKB_CB(skb)->sa.ll;
        sll->sll_family = AF_PACKET;
        sll->sll_hatype = dev->type;
        sll->sll_protocol = skb->protocol;
@@ -527,14 +538,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev, struct packet
        if (dev->hard_header_parse)
                sll->sll_halen = dev->hard_header_parse(skb, sll->sll_addr);
 
-       aux = PACKET_SKB_CB(skb);
-       aux->tp_status = TP_STATUS_USER;
-       if (skb->ip_summed == CHECKSUM_PARTIAL)
-               aux->tp_status |= TP_STATUS_CSUMNOTREADY;
-       aux->tp_len = skb->len;
-       aux->tp_snaplen = snaplen;
-       aux->tp_mac = 0;
-       aux->tp_net = skb->nh.raw - skb->data;
+       PACKET_SKB_CB(skb)->origlen = skb->len;
 
        if (pskb_trim(skb, snaplen))
                goto drop_n_acct;
@@ -1106,7 +1110,7 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
         *      it in now.
         */
 
-       sll = (struct sockaddr_ll*)skb->cb;
+       sll = &PACKET_SKB_CB(skb)->sa.ll;
        if (sock->type == SOCK_PACKET)
                msg->msg_namelen = sizeof(struct sockaddr_pkt);
        else
@@ -1131,11 +1135,21 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
        sock_recv_timestamp(msg, sk, skb);
 
        if (msg->msg_name)
-               memcpy(msg->msg_name, skb->cb, msg->msg_namelen);
+               memcpy(msg->msg_name, &PACKET_SKB_CB(skb)->sa,
+                      msg->msg_namelen);
 
        if (pkt_sk(sk)->auxdata) {
-               struct tpacket_auxdata *aux = PACKET_SKB_CB(skb);
-               put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(*aux), aux);
+               struct tpacket_auxdata aux;
+
+               aux.tp_status = TP_STATUS_USER;
+               if (skb->ip_summed == CHECKSUM_PARTIAL)
+                       aux.tp_status |= TP_STATUS_CSUMNOTREADY;
+               aux.tp_len = PACKET_SKB_CB(skb)->origlen;
+               aux.tp_snaplen = skb->len;
+               aux.tp_mac = 0;
+               aux.tp_net = skb->nh.raw - skb->data;
+
+               put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(aux), &aux);
        }
 
        /*