net: packet: use sockaddr_ll fields as storage for skb original length in recvmsg path
As part of an effort to move skb->dropcount to skb->cb[], 4 bytes
of additional room are needed in skb->cb[] in packet sockets.
Store the skb original length in the first two fields of sockaddr_ll
(sll_family and sll_protocol) as they can be derived from the skb when
needed.
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 9c28cec..7eea30b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -216,10 +216,16 @@
static void packet_flush_mclist(struct sock *sk);
struct packet_skb_cb {
- unsigned int origlen;
union {
struct sockaddr_pkt pkt;
- struct sockaddr_ll ll;
+ union {
+ /* Trick: alias skb original length with
+ * ll.sll_family and ll.protocol in order
+ * to save room.
+ */
+ unsigned int origlen;
+ struct sockaddr_ll ll;
+ };
} sa;
};
@@ -1814,9 +1820,7 @@
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;
sll->sll_pkttype = skb->pkt_type;
if (unlikely(po->origdev))
sll->sll_ifindex = orig_dev->ifindex;
@@ -1825,7 +1829,10 @@
sll->sll_halen = dev_parse_header(skb, sll->sll_addr);
- PACKET_SKB_CB(skb)->origlen = skb->len;
+ /* sll->sll_family and sll->sll_protocol are set in packet_recvmsg().
+ * Use their space for storing the original skb length.
+ */
+ PACKET_SKB_CB(skb)->sa.origlen = skb->len;
if (pskb_trim(skb, snaplen))
goto drop_n_acct;
@@ -2883,6 +2890,7 @@
struct sk_buff *skb;
int copied, err;
int vnet_hdr_len = 0;
+ unsigned int origlen = 0;
err = -EINVAL;
if (flags & ~(MSG_PEEK|MSG_DONTWAIT|MSG_TRUNC|MSG_CMSG_COMPAT|MSG_ERRQUEUE))
@@ -2982,6 +2990,15 @@
if (err)
goto out_free;
+ if (sock->type != SOCK_PACKET) {
+ struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll;
+
+ /* Original length was stored in sockaddr_ll fields */
+ origlen = PACKET_SKB_CB(skb)->sa.origlen;
+ sll->sll_family = AF_PACKET;
+ sll->sll_protocol = skb->protocol;
+ }
+
sock_recv_ts_and_drops(msg, sk, skb);
if (msg->msg_name) {
@@ -2993,6 +3010,7 @@
msg->msg_namelen = sizeof(struct sockaddr_pkt);
} else {
struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll;
+
msg->msg_namelen = sll->sll_halen +
offsetof(struct sockaddr_ll, sll_addr);
}
@@ -3006,7 +3024,7 @@
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_len = origlen;
aux.tp_snaplen = skb->len;
aux.tp_mac = 0;
aux.tp_net = skb_network_offset(skb);
