net-timestamp: allow reading recv cmsg on errqueue with origin tstamp

Allow reading of timestamps and cmsg at the same time on all relevant
socket families. One use is to correlate timestamps with egress
device, by asking for cmsg IP_PKTINFO.

on AF_INET sockets, call the relevant function (ip_cmsg_recv). To
avoid changing legacy expectations, only do so if the caller sets a
new timestamping flag SOF_TIMESTAMPING_OPT_CMSG.

on AF_INET6 sockets, IPV6_PKTINFO and all other recv cmsg are already
returned for all origins. only change is to set ifindex, which is
not initialized for all error origins.

In both cases, only generate the pktinfo message if an ifindex is
known. This is not the case for ACK timestamps.

The difference between the protocol families is probably a historical
accident as a result of the different conditions for generating cmsg
in the relevant ip(v6)_recv_error function:

ipv4:        if (serr->ee.ee_origin == SO_EE_ORIGIN_ICMP) {
ipv6:        if (serr->ee.ee_origin != SO_EE_ORIGIN_LOCAL) {

At one time, this was the same test bar for the ICMP/ICMP6
distinction. This is no longer true.

Signed-off-by: Willem de Bruijn <willemb@google.com>

----

Changes
  v1 -> v2
    large rewrite
    - integrate with existing pktinfo cmsg generation code
    - on ipv4: only send with new flag, to maintain legacy behavior
    - on ipv6: send at most a single pktinfo cmsg
    - on ipv6: initialize fields if not yet initialized

The recv cmsg interfaces are also relevant to the discussion of
whether looping packet headers is problematic. For v6, cmsgs that
identify many headers are already returned. This patch expands
that to v4. If it sounds reasonable, I will follow with patches

1. request timestamps without payload with SOF_TIMESTAMPING_OPT_TSONLY
   (http://patchwork.ozlabs.org/patch/366967/)
2. sysctl to conditionally drop all timestamps that have payload or
   cmsg from users without CAP_NET_RAW.
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 2 deletions

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 59eba6c7a51..640f26c6a9f 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -399,6 +399,22 @@ void ip_local_error(struct sock *sk, int err, __be32 daddr, __be16 port, u32 inf
 		kfree_skb(skb);
 }
 
+static bool ipv4_pktinfo_prepare_errqueue(const struct sock *sk,
+					  const struct sk_buff *skb,
+					  int ee_origin)
+{
+	struct in_pktinfo *info = PKTINFO_SKB_CB(skb);
+
+	if ((ee_origin != SO_EE_ORIGIN_TIMESTAMPING) ||
+	    (!(sk->sk_tsflags & SOF_TIMESTAMPING_OPT_CMSG)) ||
+	    (!skb->dev))
+		return false;
+
+	info->ipi_spec_dst.s_addr = ip_hdr(skb)->saddr;
+	info->ipi_ifindex = skb->dev->ifindex;
+	return true;
+}
+
 /*
  *	Handle MSG_ERRQUEUE
  */
@@ -446,7 +462,9 @@ int ip_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 	memcpy(&errhdr.ee, &serr->ee, sizeof(struct sock_extended_err));
 	sin = &errhdr.offender;
 	sin->sin_family = AF_UNSPEC;
-	if (serr->ee.ee_origin == SO_EE_ORIGIN_ICMP) {
+
+	if (serr->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
+	    ipv4_pktinfo_prepare_errqueue(sk, skb, serr->ee.ee_origin)) {
 		struct inet_sock *inet = inet_sk(sk);
 
 		sin->sin_family = AF_INET;
@@ -1051,7 +1069,7 @@ e_inval:
 }
 
 /**
- * ipv4_pktinfo_prepare - transfert some info from rtable to skb
+ * ipv4_pktinfo_prepare - transfer some info from rtable to skb
  * @sk: socket
  * @skb: buffer
  *