[PATCH net-next v3 0/3] net-timestamp: blinding

[PATCH net-next v3 0/3] net-timestamp: blinding

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

Changes
  (v2 -> v3)
  - rebase only: v2 did not make it to patchwork / netdev
  (v1 -> v2)
  - fix capability check in patch 2
      this could be moved into net/core/sock.c as sk_capable_nouser()
  (rfc -> v1)
  - dropped patch 4: timestamp batching
      due to complexity, as discussed
  - dropped patch 5: default mode
      because it does not really cover all use cases, as discussed
  - added documentation
  - minor fix, see patch 2


Two issues were raised during recent timestamping discussions:
1. looping full packets on the error queue exposes packet headers
2. TCP timestamping with retransmissions generates many timestamps

This RFC patchset is an attempt at addressing both without breaking
legacy behavior.

Patch 1 reintroduces the "no payload" timestamp option, which loops
timestamps onto an empty skb. This reduces the pressure on SO_RCVBUF
from looping many timestamps. It does not reduce the number of recv()
calls needed to process them. The timestamp cookie mechanism developed
in http://patchwork.ozlabs.org/patch/427213/ did, but this is
considerably simpler.

Patch 2 then gives administrators the power to block all timestamp
requests that contain data by unprivileged users. I proposed this
earlier as a backward compatible workaround in the discussion of

  net-timestamp: pull headers for SOCK_STREAM
  http://patchwork.ozlabs.org/patch/414810/

Patch 3 only updates the txtimestamp example to test this option.
Verified that with option '-n', length is zero in all cases and
option '-I' (PKTINFO) stops working.


Willem de Bruijn (3):
  net-timestamp: no-payload option
  net-timestamp: no-payload only sysctl
  net-timestamp: no-payload option in txtimestamp test

 Documentation/networking/timestamping.txt          | 21 ++++++++++++
 .../networking/timestamping/txtimestamp.c          | 28 ++++++++++++---
 Documentation/sysctl/net.txt                       |  8 +++++
 include/net/sock.h                                 |  1 +
 include/uapi/linux/net_tstamp.h                    |  3 +-
 net/core/skbuff.c                                  | 40 ++++++++++++++++++----
 net/core/sock.c                                    |  3 ++
 net/core/sysctl_net_core.c                         |  9 +++++
 net/ipv4/ip_sockglue.c                             |  7 ++--
 net/ipv6/datagram.c                                |  5 ++-
 net/rxrpc/ar-error.c                               |  5 +++
 11 files changed, 113 insertions(+), 17 deletions(-)

-- 
2.2.0.rc0.207.ga3a616c

[PATCH net-next v3 1/3] net-timestamp: no-payload option

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

Add timestamping option SOF_TIMESTAMPING_OPT_TSONLY. For transmit
timestamps, this loops timestamps on top of empty packets.

Doing so reduces the pressure on SO_RCVBUF. Payload inspection and
cmsg reception (aside from timestamps) are no longer possible. This
works together with a follow on patch that allows administrators to
only allow tx timestamping if it does not loop payload or metadata.

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

----

Changes (rfc -> v1)
  - add documentation
  - remove unnecessary skb->len test (thanks to Richard Cochran)
---
 Documentation/networking/timestamping.txt | 21 +++++++++++++++++++++
 include/uapi/linux/net_tstamp.h           |  3 ++-
 net/core/skbuff.c                         | 19 ++++++++++++++-----
 net/ipv4/ip_sockglue.c                    |  7 ++++---
 net/ipv6/datagram.c                       |  5 ++---
 net/rxrpc/ar-error.c                      |  5 +++++
 6 files changed, 48 insertions(+), 12 deletions(-)

diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index a5c784c..5f09226 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -162,6 +162,27 @@ SOF_TIMESTAMPING_OPT_CMSG:
   option IP_PKTINFO simultaneously.
 
 
+SOF_TIMESTAMPING_OPT_TSONLY:
+
+  Applies to transmit timestamps only. Makes the kernel return the
+  timestamp as a cmsg alongside an empty packet, as opposed to
+  alongside the original packet. This reduces the amount of memory
+  charged to the socket's receive budget (SO_RCVBUF) and delivers
+  the timestamp even if sysctl net.core.tstamp_allow_data is 0.
+  This option disables SOF_TIMESTAMPING_OPT_CMSG.
+
+
+New applications are encouraged to pass SOF_TIMESTAMPING_OPT_ID to
+disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate
+regardless of the setting of sysctl net.core.tstamp_allow_data.
+
+An exception is when a process needs additional cmsg data, for
+instance SOL_IP/IP_PKTINFO to detect the egress network interface.
+Then pass option SOF_TIMESTAMPING_OPT_CMSG. This option depends on
+having access to the contents of the original packet, so cannot be
+combined with SOF_TIMESTAMPING_OPT_TSONLY.
+
+
 1.4 Bytestream Timestamps
 
 The SO_TIMESTAMPING interface supports timestamping of bytes in a
diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
index edbc888..6d1abea 100644
--- a/include/uapi/linux/net_tstamp.h
+++ b/include/uapi/linux/net_tstamp.h
@@ -24,8 +24,9 @@ enum {
 	SOF_TIMESTAMPING_TX_SCHED = (1<<8),
 	SOF_TIMESTAMPING_TX_ACK = (1<<9),
 	SOF_TIMESTAMPING_OPT_CMSG = (1<<10),
+	SOF_TIMESTAMPING_OPT_TSONLY = (1<<11),
 
-	SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_OPT_CMSG,
+	SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_OPT_TSONLY,
 	SOF_TIMESTAMPING_MASK = (SOF_TIMESTAMPING_LAST - 1) |
 				 SOF_TIMESTAMPING_LAST
 };
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 56db472..65a3798 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3710,19 +3710,28 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
 		     struct sock *sk, int tstype)
 {
 	struct sk_buff *skb;
+	bool tsonly = sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TSONLY;
 
 	if (!sk)
 		return;
 
-	if (hwtstamps)
-		*skb_hwtstamps(orig_skb) = *hwtstamps;
+	if (tsonly)
+		skb = alloc_skb(0, GFP_ATOMIC);
 	else
-		orig_skb->tstamp = ktime_get_real();
-
-	skb = skb_clone(orig_skb, GFP_ATOMIC);
+		skb = skb_clone(orig_skb, GFP_ATOMIC);
 	if (!skb)
 		return;
 
+	if (tsonly) {
+		skb_shinfo(skb)->tx_flags = skb_shinfo(orig_skb)->tx_flags;
+		skb_shinfo(skb)->tskey = skb_shinfo(orig_skb)->tskey;
+	}
+
+	if (hwtstamps)
+		*skb_hwtstamps(skb) = *hwtstamps;
+	else
+		skb->tstamp = ktime_get_real();
+
 	__skb_complete_tx_timestamp(skb, sk, tstype);
 }
 EXPORT_SYMBOL_GPL(__skb_tstamp_tx);
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index db5e0f8..31d8c71 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -483,7 +483,7 @@ int ip_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 
 	serr = SKB_EXT_ERR(skb);
 
-	if (sin) {
+	if (sin && skb->len) {
 		sin->sin_family = AF_INET;
 		sin->sin_addr.s_addr = *(__be32 *)(skb_network_header(skb) +
 						   serr->addr_offset);
@@ -496,8 +496,9 @@ int ip_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 	sin = &errhdr.offender;
 	memset(sin, 0, sizeof(*sin));
 
-	if (serr->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
-	    ipv4_pktinfo_prepare_errqueue(sk, skb, serr->ee.ee_origin)) {
+	if (skb->len &&
+	    (serr->ee.ee_origin == SO_EE_ORIGIN_ICMP ||
+	     ipv4_pktinfo_prepare_errqueue(sk, skb, serr->ee.ee_origin))) {
 		sin->sin_family = AF_INET;
 		sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
 		if (inet_sk(sk)->cmsg_flags)
diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 49f5e73..c215be7 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -369,7 +369,7 @@ int ipv6_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 
 	serr = SKB_EXT_ERR(skb);
 
-	if (sin) {
+	if (sin && skb->len) {
 		const unsigned char *nh = skb_network_header(skb);
 		sin->sin6_family = AF_INET6;
 		sin->sin6_flowinfo = 0;
@@ -394,8 +394,7 @@ int ipv6_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;
 	memset(sin, 0, sizeof(*sin));
-
-	if (serr->ee.ee_origin != SO_EE_ORIGIN_LOCAL) {
+	if (serr->ee.ee_origin != SO_EE_ORIGIN_LOCAL && skb->len) {
 		sin->sin6_family = AF_INET6;
 		if (np->rxopt.all) {
 			if (serr->ee.ee_origin != SO_EE_ORIGIN_ICMP &&
diff --git a/net/rxrpc/ar-error.c b/net/rxrpc/ar-error.c
index 74c0fcd..5394b6b 100644
--- a/net/rxrpc/ar-error.c
+++ b/net/rxrpc/ar-error.c
@@ -42,6 +42,11 @@ void rxrpc_UDP_error_report(struct sock *sk)
 		_leave("UDP socket errqueue empty");
 		return;
 	}
+	if (!skb->len) {
+		_leave("UDP empty message");
+		kfree_skb(skb);
+		return;
+	}
 
 	rxrpc_new_skb(skb);
 
-- 
2.2.0.rc0.207.ga3a616c

[PATCH net-next v3 2/3] net-timestamp: no-payload only sysctl

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

Tx timestamps are looped onto the error queue on top of an skb. This
mechanism leaks packet headers to processes unless the no-payload
options SOF_TIMESTAMPING_OPT_TSONLY is set.

Add a sysctl that optionally drops looped timestamp with data. This
only affects processes without CAP_NET_RAW.

The policy is checked when timestamps are generated in the stack.
It is possible for timestamps with data to be reported after the
sysctl is set, if these were queued internally earlier.

No vulnerability is immediately known that exploits knowledge
gleaned from packet headers, but it may still be preferable to allow
administrators to lock down this path at the cost of possible
breakage of legacy applications.

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

----

Changes
  (v1 -> v2)
  - test socket CAP_NET_RAW instead of capable(CAP_NET_RAW)
  (rfc -> v1)
  - document the sysctl in Documentation/sysctl/net.txt
  - fix access control race: read .._OPT_TSONLY only once,
        use same value for permission check and skb generation.
---
 Documentation/sysctl/net.txt |  8 ++++++++
 include/net/sock.h           |  1 +
 net/core/skbuff.c            | 21 ++++++++++++++++++++-
 net/core/sock.c              |  3 +++
 net/core/sysctl_net_core.c   |  9 +++++++++
 5 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
index 666594b..6294b51 100644
--- a/Documentation/sysctl/net.txt
+++ b/Documentation/sysctl/net.txt
@@ -97,6 +97,14 @@ rmem_max
 
 The maximum receive socket buffer size in bytes.
 
+tstamp_allow_data
+-----------------
+Allow processes to receive tx timestamps looped together with the original
+packet contents. If disabled, transmit timestamp requests from unprivileged
+processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set.
+Default: 1 (on)
+
+
 wmem_default
 ------------
 
diff --git a/include/net/sock.h b/include/net/sock.h
index 1534149..511ef7c8 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2239,6 +2239,7 @@ bool sk_net_capable(const struct sock *sk, int cap);
 extern __u32 sysctl_wmem_max;
 extern __u32 sysctl_rmem_max;
 
+extern int sysctl_tstamp_allow_data;
 extern int sysctl_optmem_max;
 
 extern __u32 sysctl_wmem_default;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 65a3798..a5bff27 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -74,6 +74,8 @@
 #include <asm/uaccess.h>
 #include <trace/events/skb.h>
 #include <linux/highmem.h>
+#include <linux/capability.h>
+#include <linux/user_namespace.h>
 
 struct kmem_cache *skbuff_head_cache __read_mostly;
 static struct kmem_cache *skbuff_fclone_cache __read_mostly;
@@ -3690,11 +3692,28 @@ static void __skb_complete_tx_timestamp(struct sk_buff *skb,
 		kfree_skb(skb);
 }
 
+static bool skb_may_tx_timestamp(struct sock *sk, bool tsonly)
+{
+	bool ret;
+
+	if (likely(sysctl_tstamp_allow_data || tsonly))
+		return true;
+
+	read_lock_bh(&sk->sk_callback_lock);
+	ret = sk->sk_socket && sk->sk_socket->file &&
+	      file_ns_capable(sk->sk_socket->file, &init_user_ns, CAP_NET_RAW);
+	read_unlock_bh(&sk->sk_callback_lock);
+	return ret;
+}
+
 void skb_complete_tx_timestamp(struct sk_buff *skb,
 			       struct skb_shared_hwtstamps *hwtstamps)
 {
 	struct sock *sk = skb->sk;
 
+	if (!skb_may_tx_timestamp(sk, false))
+		return;
+
 	/* take a reference to prevent skb_orphan() from freeing the socket */
 	sock_hold(sk);
 
@@ -3712,7 +3731,7 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
 	struct sk_buff *skb;
 	bool tsonly = sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TSONLY;
 
-	if (!sk)
+	if (!sk || !skb_may_tx_timestamp(sk, tsonly))
 		return;
 
 	if (tsonly)
diff --git a/net/core/sock.c b/net/core/sock.c
index 1c7a33d..93c8b20 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -325,6 +325,8 @@ __u32 sysctl_rmem_default __read_mostly = SK_RMEM_MAX;
 int sysctl_optmem_max __read_mostly = sizeof(unsigned long)*(2*UIO_MAXIOV+512);
 EXPORT_SYMBOL(sysctl_optmem_max);
 
+int sysctl_tstamp_allow_data __read_mostly = 1;
+
 struct static_key memalloc_socks = STATIC_KEY_INIT_FALSE;
 EXPORT_SYMBOL_GPL(memalloc_socks);
 
@@ -840,6 +842,7 @@ set_rcvbuf:
 			ret = -EINVAL;
 			break;
 		}
+
 		if (val & SOF_TIMESTAMPING_OPT_ID &&
 		    !(sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)) {
 			if (sk->sk_protocol == IPPROTO_TCP) {
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 31baba2..fde21d1 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -321,6 +321,15 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+	{
+		.procname	= "tstamp_allow_data",
+		.data		= &sysctl_tstamp_allow_data,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one
+	},
 #ifdef CONFIG_RPS
 	{
 		.procname	= "rps_sock_flow_entries",
-- 
2.2.0.rc0.207.ga3a616c

[PATCH net-next v3 3/3] net-timestamp: no-payload option in txtimestamp test

[Willem de Bruijn]

From: Willem de Bruijn <willemb@google.com>

Demonstrate how SOF_TIMESTAMPING_OPT_TSONLY can be used and
test the implementation.

Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 .../networking/timestamping/txtimestamp.c          | 28 ++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/timestamping/txtimestamp.c b/Documentation/networking/timestamping/txtimestamp.c
index 05694fe..8217510 100644
--- a/Documentation/networking/timestamping/txtimestamp.c
+++ b/Documentation/networking/timestamping/txtimestamp.c
@@ -70,6 +70,7 @@ static int do_ipv6 = 1;
 static int cfg_payload_len = 10;
 static bool cfg_show_payload;
 static bool cfg_do_pktinfo;
+static bool cfg_loop_nodata;
 static uint16_t dest_port = 9000;
 
 static struct sockaddr_in daddr;
@@ -141,6 +142,9 @@ static void print_payload(char *data, int len)
 {
 	int i;
 
+	if (!len)
+		return;
+
 	if (len > 70)
 		len = 70;
 
@@ -177,6 +181,7 @@ static void __recv_errmsg_cmsg(struct msghdr *msg, int payload_len)
 	struct sock_extended_err *serr = NULL;
 	struct scm_timestamping *tss = NULL;
 	struct cmsghdr *cm;
+	int batch = 0;
 
 	for (cm = CMSG_FIRSTHDR(msg);
 	     cm && cm->cmsg_len;
@@ -209,10 +214,18 @@ static void __recv_errmsg_cmsg(struct msghdr *msg, int payload_len)
 		} else
 			fprintf(stderr, "unknown cmsg %d,%d\n",
 					cm->cmsg_level, cm->cmsg_type);
+
+		if (serr && tss) {
+			print_timestamp(tss, serr->ee_info, serr->ee_data,
+					payload_len);
+			serr = NULL;
+			tss = NULL;
+			batch++;
+		}
 	}
 
-	if (serr && tss)
-		print_timestamp(tss, serr->ee_info, serr->ee_data, payload_len);
+	if (batch > 1)
+		fprintf(stderr, "batched %d timestamps\n", batch);
 }
 
 static int recv_errmsg(int fd)
@@ -244,7 +257,7 @@ static int recv_errmsg(int fd)
 	if (ret == -1 && errno != EAGAIN)
 		error(1, errno, "recvmsg");
 
-	if (ret > 0) {
+	if (ret >= 0) {
 		__recv_errmsg_cmsg(&msg, ret);
 		if (cfg_show_payload)
 			print_payload(data, cfg_payload_len);
@@ -309,6 +322,9 @@ static void do_test(int family, unsigned int opt)
 	opt |= SOF_TIMESTAMPING_SOFTWARE |
 	       SOF_TIMESTAMPING_OPT_CMSG |
 	       SOF_TIMESTAMPING_OPT_ID;
+	if (cfg_loop_nodata)
+		opt |= SOF_TIMESTAMPING_OPT_TSONLY;
+
 	if (setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING,
 		       (char *) &opt, sizeof(opt)))
 		error(1, 0, "setsockopt timestamping");
@@ -378,6 +394,7 @@ static void __attribute__((noreturn)) usage(const char *filepath)
 			"  -h:   show this message\n"
 			"  -I:   request PKTINFO\n"
 			"  -l N: send N bytes at a time\n"
+			"  -n:   set no-payload option\n"
 			"  -r:   use raw\n"
 			"  -R:   use raw (IP_HDRINCL)\n"
 			"  -p N: connect to port N\n"
@@ -392,7 +409,7 @@ static void parse_opt(int argc, char **argv)
 	int proto_count = 0;
 	char c;
 
-	while ((c = getopt(argc, argv, "46hIl:p:rRux")) != -1) {
+	while ((c = getopt(argc, argv, "46hIl:np:rRux")) != -1) {
 		switch (c) {
 		case '4':
 			do_ipv6 = 0;
@@ -403,6 +420,9 @@ static void parse_opt(int argc, char **argv)
 		case 'I':
 			cfg_do_pktinfo = true;
 			break;
+		case 'n':
+			cfg_loop_nodata = true;
+			break;
 		case 'r':
 			proto_count++;
 			cfg_proto = SOCK_RAW;
-- 
2.2.0.rc0.207.ga3a616c

Re: [PATCH net-next v3 0/3] net-timestamp: blinding

[Richard Cochran]

On Fri, Jan 30, 2015 at 01:29:30PM -0500, Willem de Bruijn wrote:
> Two issues were raised during recent timestamping discussions:
> 1. looping full packets on the error queue exposes packet headers
> 2. TCP timestamping with retransmissions generates many timestamps

For the series,

Acked-by: Richard Cochran <richardcochran@gmail.com>

Re: [PATCH net-next v3 0/3] net-timestamp: blinding

[David Miller]

From: Richard Cochran <richardcochran@gmail.com>
Date: Sun, 1 Feb 2015 12:29:31 +0100

> On Fri, Jan 30, 2015 at 01:29:30PM -0500, Willem de Bruijn wrote:
>> Two issues were raised during recent timestamping discussions:
>> 1. looping full packets on the error queue exposes packet headers
>> 2. TCP timestamping with retransmissions generates many timestamps
> 
> For the series,
> 
> Acked-by: Richard Cochran <richardcochran@gmail.com>

Series applied, thanks everyone.