sock: accept SO_TIMESTAMPING flags in socket cmsg

Accept SO_TIMESTAMPING in control messages of the SOL_SOCKET level
as a basis to accept timestamping requests per write.

This implementation only accepts TX recording flags (i.e.,
SOF_TIMESTAMPING_TX_HARDWARE, SOF_TIMESTAMPING_TX_SOFTWARE,
SOF_TIMESTAMPING_TX_SCHED, and SOF_TIMESTAMPING_TX_ACK) in
control messages. Users need to set reporting flags (e.g.,
SOF_TIMESTAMPING_OPT_ID) per socket via socket options.

This commit adds a tsflags field in sockcm_cookie which is
set in __sock_cmsg_send. It only override the SOF_TIMESTAMPING_TX_*
bits in sockcm_cookie.tsflags allowing the control message
to override the recording behavior per write, yet maintaining
the value of other flags.

This patch implements validating the control message and setting
tsflags in struct sockcm_cookie. Next commits in this series will
actually implement timestamping per write for different protocols.
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1418,6 +1418,7 @@ void sk_send_sigurg(struct sock *sk);
 
 struct sockcm_cookie {
 	u32 mark;
+	u16 tsflags;
 };
 
 int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg,

include/uapi/linux/net_tstamp.h

@@ -31,6 +31,16 @@ enum {
 				 SOF_TIMESTAMPING_LAST
 };
 
+/*
+ * SO_TIMESTAMPING flags are either for recording a packet timestamp or for
+ * reporting the timestamp to user space.
+ * Recording flags can be set both via socket options and control messages.
+ */
+#define SOF_TIMESTAMPING_TX_RECORD_MASK	(SOF_TIMESTAMPING_TX_HARDWARE | \
+					 SOF_TIMESTAMPING_TX_SOFTWARE | \
+					 SOF_TIMESTAMPING_TX_SCHED | \
+					 SOF_TIMESTAMPING_TX_ACK)
+
 /**
  * struct hwtstamp_config - %SIOCGHWTSTAMP and %SIOCSHWTSTAMP parameter
  *

net/core/sock.c

@@ -1870,6 +1870,8 @@ EXPORT_SYMBOL(sock_alloc_send_skb);
 int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg,
 		     struct sockcm_cookie *sockc)
 {
+	u32 tsflags;
+
 	switch (cmsg->cmsg_type) {
 	case SO_MARK:
 		if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
@@ -1878,6 +1880,17 @@ int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg,
 			return -EINVAL;
 		sockc->mark = *(u32 *)CMSG_DATA(cmsg);
 		break;
+	case SO_TIMESTAMPING:
+		if (cmsg->cmsg_len != CMSG_LEN(sizeof(u32)))
+			return -EINVAL;
+
+		tsflags = *(u32 *)CMSG_DATA(cmsg);
+		if (tsflags & ~SOF_TIMESTAMPING_TX_RECORD_MASK)
+			return -EINVAL;
+
+		sockc->tsflags &= ~SOF_TIMESTAMPING_TX_RECORD_MASK;
+		sockc->tsflags |= tsflags;
+		break;
 	default:
 		return -EINVAL;
 	}