[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>

1 files changed, 30 insertions, 16 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 8973ea78831e..a6fa48788e8f 100644
--- 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);
         }
 
         /*