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connector: fix out-of-order cn_proc netlink message delivery
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The proc connector messages include a sequence number, allowing userspace
programs to detect lost messages.  However, performing this detection is
currently more difficult than necessary, since netlink messages can be
delivered to the application out-of-order.  To fix this, leave pre-emption
disabled during cn_netlink_send(), and use GFP_NOWAIT.

The following was written as a test case.  Building the kernel w/ make -j32
proved a reliable way to generate out-of-order cn_proc messages.

int
main(int argc, char *argv[])
{
	static uint32_t last_seq[CPU_SETSIZE], seq;
	int cpu, fd;
	struct sockaddr_nl sa;
	struct __attribute__((aligned(NLMSG_ALIGNTO))) {
		struct nlmsghdr nl_hdr;
		struct __attribute__((__packed__)) {
			struct cn_msg cn_msg;
			struct proc_event cn_proc;
		};
	} rmsg;
	struct __attribute__((aligned(NLMSG_ALIGNTO))) {
		struct nlmsghdr nl_hdr;
		struct __attribute__((__packed__)) {
			struct cn_msg cn_msg;
			enum proc_cn_mcast_op cn_mcast;
		};
	} smsg;

	fd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
	if (fd < 0) {
		perror("socket");
	}

	sa.nl_family = AF_NETLINK;
	sa.nl_groups = CN_IDX_PROC;
	sa.nl_pid = getpid();
	if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
		perror("bind");
	}

	memset(&smsg, 0, sizeof(smsg));
	smsg.nl_hdr.nlmsg_len = sizeof(smsg);
	smsg.nl_hdr.nlmsg_pid = getpid();
	smsg.nl_hdr.nlmsg_type = NLMSG_DONE;
	smsg.cn_msg.id.idx = CN_IDX_PROC;
	smsg.cn_msg.id.val = CN_VAL_PROC;
	smsg.cn_msg.len = sizeof(enum proc_cn_mcast_op);
	smsg.cn_mcast = PROC_CN_MCAST_LISTEN;
	if (send(fd, &smsg, sizeof(smsg), 0) != sizeof(smsg)) {
		perror("send");
	}

	while (recv(fd, &rmsg, sizeof(rmsg), 0) == sizeof(rmsg)) {
		cpu = rmsg.cn_proc.cpu;
		if (cpu < 0) {
			continue;
		}
		seq = rmsg.cn_msg.seq;
		if ((last_seq[cpu] != 0) && (seq != last_seq[cpu] + 1)) {
			printf("out-of-order seq=%d on cpu=%d\n", seq, cpu);
		}
		last_seq[cpu] = seq;
	}

	/* NOTREACHED */

	perror("recv");

	return -1;
}

Signed-off-by: Aaron Campbell <aaron@monkey.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@aarcamp @davem330
aarcamp authored and davem330 committed Jun 28, 2016
1 parent 0888d5f commit ab8ed95
Showing 1 changed file with 22 additions and 21 deletions.
43 changes: 22 additions & 21 deletions drivers/connector/cn_proc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -56,11 +56,21 @@ static struct cb_id cn_proc_event_id = { CN_IDX_PROC, CN_VAL_PROC };
/* proc_event_counts is used as the sequence number of the netlink message */
static DEFINE_PER_CPU(__u32, proc_event_counts) = { 0 };

static inline void get_seq(__u32 *ts, int *cpu)
static inline void send_msg(struct cn_msg *msg)
{
preempt_disable();
*ts = __this_cpu_inc_return(proc_event_counts) - 1;
*cpu = smp_processor_id();

msg->seq = __this_cpu_inc_return(proc_event_counts) - 1;
((struct proc_event *)msg->data)->cpu = smp_processor_id();

/*
* Preemption remains disabled during send to ensure the messages are
* ordered according to their sequence numbers.
*
* If cn_netlink_send() fails, the data is not sent.
*/
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_NOWAIT);

preempt_enable();
}

Expand All @@ -77,7 +87,6 @@ void proc_fork_connector(struct task_struct *task)
msg = buffer_to_cn_msg(buffer);
ev = (struct proc_event *)msg->data;
memset(&ev->event_data, 0, sizeof(ev->event_data));
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();
ev->what = PROC_EVENT_FORK;
rcu_read_lock();
Expand All @@ -92,8 +101,7 @@ void proc_fork_connector(struct task_struct *task)
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
/* If cn_netlink_send() failed, the data is not sent */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

void proc_exec_connector(struct task_struct *task)
Expand All @@ -108,7 +116,6 @@ void proc_exec_connector(struct task_struct *task)
msg = buffer_to_cn_msg(buffer);
ev = (struct proc_event *)msg->data;
memset(&ev->event_data, 0, sizeof(ev->event_data));
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();
ev->what = PROC_EVENT_EXEC;
ev->event_data.exec.process_pid = task->pid;
Expand All @@ -118,7 +125,7 @@ void proc_exec_connector(struct task_struct *task)
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

void proc_id_connector(struct task_struct *task, int which_id)
Expand Down Expand Up @@ -150,14 +157,13 @@ void proc_id_connector(struct task_struct *task, int which_id)
return;
}
rcu_read_unlock();
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();

memcpy(&msg->id, &cn_proc_event_id, sizeof(msg->id));
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

void proc_sid_connector(struct task_struct *task)
Expand All @@ -172,7 +178,6 @@ void proc_sid_connector(struct task_struct *task)
msg = buffer_to_cn_msg(buffer);
ev = (struct proc_event *)msg->data;
memset(&ev->event_data, 0, sizeof(ev->event_data));
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();
ev->what = PROC_EVENT_SID;
ev->event_data.sid.process_pid = task->pid;
Expand All @@ -182,7 +187,7 @@ void proc_sid_connector(struct task_struct *task)
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

void proc_ptrace_connector(struct task_struct *task, int ptrace_id)
Expand All @@ -197,7 +202,6 @@ void proc_ptrace_connector(struct task_struct *task, int ptrace_id)
msg = buffer_to_cn_msg(buffer);
ev = (struct proc_event *)msg->data;
memset(&ev->event_data, 0, sizeof(ev->event_data));
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();
ev->what = PROC_EVENT_PTRACE;
ev->event_data.ptrace.process_pid = task->pid;
Expand All @@ -215,7 +219,7 @@ void proc_ptrace_connector(struct task_struct *task, int ptrace_id)
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

void proc_comm_connector(struct task_struct *task)
Expand All @@ -230,7 +234,6 @@ void proc_comm_connector(struct task_struct *task)
msg = buffer_to_cn_msg(buffer);
ev = (struct proc_event *)msg->data;
memset(&ev->event_data, 0, sizeof(ev->event_data));
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();
ev->what = PROC_EVENT_COMM;
ev->event_data.comm.process_pid = task->pid;
Expand All @@ -241,7 +244,7 @@ void proc_comm_connector(struct task_struct *task)
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

void proc_coredump_connector(struct task_struct *task)
Expand All @@ -256,7 +259,6 @@ void proc_coredump_connector(struct task_struct *task)
msg = buffer_to_cn_msg(buffer);
ev = (struct proc_event *)msg->data;
memset(&ev->event_data, 0, sizeof(ev->event_data));
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();
ev->what = PROC_EVENT_COREDUMP;
ev->event_data.coredump.process_pid = task->pid;
Expand All @@ -266,7 +268,7 @@ void proc_coredump_connector(struct task_struct *task)
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

void proc_exit_connector(struct task_struct *task)
Expand All @@ -281,7 +283,6 @@ void proc_exit_connector(struct task_struct *task)
msg = buffer_to_cn_msg(buffer);
ev = (struct proc_event *)msg->data;
memset(&ev->event_data, 0, sizeof(ev->event_data));
get_seq(&msg->seq, &ev->cpu);
ev->timestamp_ns = ktime_get_ns();
ev->what = PROC_EVENT_EXIT;
ev->event_data.exit.process_pid = task->pid;
Expand All @@ -293,7 +294,7 @@ void proc_exit_connector(struct task_struct *task)
msg->ack = 0; /* not used */
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

/*
Expand Down Expand Up @@ -325,7 +326,7 @@ static void cn_proc_ack(int err, int rcvd_seq, int rcvd_ack)
msg->ack = rcvd_ack + 1;
msg->len = sizeof(*ev);
msg->flags = 0; /* not used */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_KERNEL);
send_msg(msg);
}

/**
Expand Down

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