Combine parent state traversal w/ loop detection

Replace the ad-hoc parent thread state traversal that was in several
filterchecks as well as in the mesos/coreos code with a central way to
traverse parent thread state and detect potential loops at the same
time. A new method traverse_parent_state traverses the parent state from
the current thead and takes a function that is called for each thread
while traversing.

This prevents infinite loops like observed in
falcosecurity/falco#208.

This doesn't address the underlying cause of what caused the thread
state to get corrupted in the first place. That's tracked by a separate
issue #752.

In the 4 filterchecks that used to traverse parent state (proc.sname,
proc.loginshellid, proc.aname, proc.apid), replace the direct traversal
with a call to traverse_parent_state + an appropriate visitor
function.

Update mesos's get_env_mesos_task_id, which used to do a combination of
recursion and get_parent_task_id to traverse parent state, with a visitor
and traverse_parent_state. It stops as soon as any of the environment
variables for a thread are found.

This version doesn't explicitly skip pid 1, but I don't think that was
strictly necessary as init wouldn't have those environment variables
anyway.

Also replace a similar process in coreos to find rkt pods.

userspace/libsinsp/container.cpp

@@ -157,22 +157,29 @@ sinsp_container_info* sinsp_container_manager::get_container(const string& conta
 string sinsp_container_manager::get_env_mesos_task_id(sinsp_threadinfo* tinfo)
 {
 	string mtid;
-	if(tinfo)
+
+	sinsp_threadinfo::visitor_func_t visitor = [&mtid] (sinsp_threadinfo *ptinfo)
 	{
 		// Mesos task ID detection is not a straightforward task;
 		// this list may have to be extended.
-		mtid = tinfo->get_env("MESOS_TASK_ID"); // Marathon
-		if(!mtid.empty()) { return mtid; }
-		mtid = tinfo->get_env("mesos_task_id"); // Chronos
-		if(!mtid.empty()) { return mtid; }
-		mtid = tinfo->get_env("MESOS_EXECUTOR_ID"); // others
-		if(!mtid.empty()) { return mtid; }
-		sinsp_threadinfo* ptinfo = tinfo->get_parent_thread();
-		if(ptinfo && ptinfo->m_tid > 1)
-		{
-			mtid = get_env_mesos_task_id(ptinfo);
-		}
+		mtid = ptinfo->get_env("MESOS_TASK_ID"); // Marathon
+		if(!mtid.empty()) { return false; }
+		mtid = ptinfo->get_env("mesos_task_id"); // Chronos
+		if(!mtid.empty()) { return false; }
+		mtid = ptinfo->get_env("MESOS_EXECUTOR_ID"); // others
+		if(!mtid.empty()) { return false; }
+
+		return true;
+	};
+
+	// Try the current thread first. visitor returns true if mtid
+	// was not filled in. In this case we should traverse the
+	// parents.
+	if(tinfo && visitor(tinfo))
+	{
+		tinfo->traverse_parent_state(visitor);
 	}
+
 	return mtid;
 }
 
@@ -361,10 +368,10 @@ bool sinsp_container_manager::resolve_container(sinsp_threadinfo* tinfo, bool qu
 			{
 				rkt_appname = tinfo->m_root.substr(prefix + COREOS_PREFIX.size(), suffix - prefix - COREOS_PREFIX.size());
 				// It is a rkt pod with stage1-coreos
-				sinsp_threadinfo* tinfo_it = tinfo;
-				while(!valid_id && tinfo_it != nullptr)
+
+				sinsp_threadinfo::visitor_func_t visitor = [&rkt_podid, &container_info, &rkt_appname, &valid_id] (sinsp_threadinfo *ptinfo)
 				{
-					for(const auto& env_var : tinfo_it->m_env)
+					for(const auto& env_var : ptinfo->m_env)
 					{
 						auto container_uuid_pos = env_var.find(COREOS_PODID_VAR);
 						if(container_uuid_pos == 0)
@@ -374,10 +381,17 @@ bool sinsp_container_manager::resolve_container(sinsp_threadinfo* tinfo, bool qu
 							container_info.m_id = rkt_podid + ":" + rkt_appname;
 							container_info.m_name = rkt_appname;
 							valid_id = true;
-							break;
+							return false;
 						}
 					}
-					tinfo_it = tinfo_it->get_parent_thread();
+					return true;
+				};
+
+				// Try the current thread first. visitor returns true if no coreos pid
+				// info was found. In this case we traverse the parents.
+				if (visitor(tinfo))
+				{
+					tinfo->traverse_parent_state(visitor);
 				}
 			}
 		}

userspace/libsinsp/filterchecks.cpp

@@ -1635,18 +1635,26 @@ uint8_t* sinsp_filter_check_thread::extract(sinsp_evt *evt, OUT uint32_t* len, b
 				// Find the highest ancestor process that has the same session id and
 				// declare it to be the session leader.
 				sinsp_threadinfo* mt = tinfo->get_main_thread();
-				sinsp_threadinfo* pt = NULL;
 
 				if(mt == NULL)
 				{
 					return NULL;
 				}
 
-				for(pt = mt->get_parent_thread();
-				    pt != NULL && pt->m_sid == mt->m_sid;
-				    mt = pt, pt = pt->get_parent_thread());
+				int64_t sid = mt->m_sid;
+				sinsp_threadinfo::visitor_func_t visitor = [sid, &mt] (sinsp_threadinfo *pt)
+				{
+					if(pt->m_sid != sid)
+					{
+						return false;
+					}
+					mt = pt;
+					return true;
+				};
+
+				mt->traverse_parent_state(visitor);
 
-				// At this point pt either doesn't exist or has a different session id.
+				// mt has been updated to the highest process that has the same session id.
 				// mt's comm is considered the session leader.
 				m_tstr = mt->get_comm();
 				*len = m_tstr.size();
@@ -1916,15 +1924,23 @@ uint8_t* sinsp_filter_check_thread::extract(sinsp_evt *evt, OUT uint32_t* len, b
 				}
 			}
 
-			for(; mt != NULL; mt = mt->get_parent_thread())
+			sinsp_threadinfo::visitor_func_t check_thread_for_shell = [&res] (sinsp_threadinfo *pt)
 			{
-				size_t len = mt->m_comm.size();
+				size_t len = pt->m_comm.size();
 
-				if(len >= 2 && mt->m_comm[len - 2] == 's' && mt->m_comm[len - 1] == 'h')
+				if(len >= 2 && pt->m_comm[len - 2] == 's' && pt->m_comm[len - 1] == 'h')
 				{
-					res = &mt->m_pid;
+					res = &pt->m_pid;
 				}
-			}
+
+				return true;
+			};
+
+			// First call the visitor on the main thread.
+			check_thread_for_shell(mt);
+
+			// Then check all its parents to see if they are shells
+			mt->traverse_parent_state(check_thread_for_shell);
 
 			return (uint8_t*)res;
 		}
@@ -2140,9 +2156,6 @@ uint8_t* sinsp_filter_check_thread::extract(sinsp_evt *evt, OUT uint32_t* len, b
 
 bool sinsp_filter_check_thread::compare_full_apid(sinsp_evt *evt)
 {
-	bool res;
-	uint32_t j;
-
 	sinsp_threadinfo* tinfo = evt->get_thread_info();
 
 	if(tinfo == NULL)
@@ -2169,29 +2182,33 @@ bool sinsp_filter_check_thread::compare_full_apid(sinsp_evt *evt)
 	//
 	// No id specified, search in all of the ancestors
 	//
-	for(j = 0; mt != NULL; mt = mt->get_parent_thread(), j++)
+	bool found = false;
+	sinsp_threadinfo::visitor_func_t visitor = [this, &found] (sinsp_threadinfo *pt)
 	{
-		if(j > 0)
+		bool res;
+
+		res = flt_compare(m_cmpop,
+				  PT_PID,
+				  &pt->m_pid);
+
+		if(res == true)
 		{
-			res = flt_compare(m_cmpop,
-				PT_PID,
-				&mt->m_pid);
+			found = true;
 
-			if(res == true)
-			{
-				return true;
-			}
+			// Can stop traversing parent state
+			return false;
 		}
-	}
 
-	return false;
+		return true;
+	};
+
+	mt->traverse_parent_state(visitor);
+
+	return found;
 }
 
 bool sinsp_filter_check_thread::compare_full_aname(sinsp_evt *evt)
 {
-	bool res;
-	uint32_t j;
-
 	sinsp_threadinfo* tinfo = evt->get_thread_info();
 
 	if(tinfo == NULL)
@@ -2218,22 +2235,29 @@ bool sinsp_filter_check_thread::compare_full_aname(sinsp_evt *evt)
 	//
 	// No id specified, search in all of the ancestors
 	//
-	for(j = 0; mt != NULL; mt = mt->get_parent_thread(), j++)
+	bool found = false;
+	sinsp_threadinfo::visitor_func_t visitor = [this, &found] (sinsp_threadinfo *pt)
 	{
-		if(j > 0)
+		bool res;
+
+		res = flt_compare(m_cmpop,
+				  PT_CHARBUF,
+				  (void*)pt->m_comm.c_str());
+
+		if(res == true)
 		{
-			res = flt_compare(m_cmpop,
-				PT_CHARBUF,
-				(void*)mt->m_comm.c_str());
+			found = true;
 
-			if(res == true)
-			{
-				return true;
-			}
+			// Can stop traversing parent state
+			return false;
 		}
-	}
 
-	return false;
+		return true;
+	};
+
+	mt->traverse_parent_state(visitor);
+
+	return found;
 }
 
 bool sinsp_filter_check_thread::compare(sinsp_evt *evt)

userspace/libsinsp/threadinfo.cpp

@@ -86,6 +86,7 @@ void sinsp_threadinfo::init()
 	m_program_hash = 0;
 	m_program_hash_falco = 0;
 	m_lastevent_data = NULL;
+	m_parent_loop_detected = false;
 }
 
 sinsp_threadinfo::~sinsp_threadinfo()
@@ -767,6 +768,49 @@ uint64_t sinsp_threadinfo::get_fd_limit()
 	return get_main_thread()->m_fdlimit;
 }
 
+void sinsp_threadinfo::traverse_parent_state(visitor_func_t &visitor)
+{
+	// Use two pointers starting at this, traversing the parent
+	// state, at different rates. If they ever equal each other
+	// before slow is NULL there's a loop.
+
+	sinsp_threadinfo *slow=this->get_parent_thread(), *fast=slow;
+
+	// Move fast to its parent
+	fast = (fast ? fast->get_parent_thread() : fast);
+
+	while(slow)
+	{
+		if(!visitor(slow))
+		{
+			break;
+		}
+
+		// Advance slow one step and advance fast two steps
+		slow = slow->get_parent_thread();
+
+		// advance fast 2 steps, checking to see if we meet
+		// slow after each step.
+		for (uint32_t i = 0; i < 2; i++) {
+			fast = (fast ? fast->get_parent_thread() : fast);
+
+			// If not at the end but fast == slow, there's a loop
+			// in the thread state.
+			if(slow && (slow == fast))
+			{
+				// Note we only log a loop once for a given main thread, to avoid flooding logs.
+				if(!m_parent_loop_detected)
+				{
+					g_logger.log(string("Loop in parent thread state detected for pid ") +
+						     std::to_string(m_pid), sinsp_logger::SEV_WARNING);
+					m_parent_loop_detected = true;
+				}
+				return;
+			}
+		}
+	}
+}
+
 sinsp_threadinfo* sinsp_threadinfo::lookup_thread()
 {
 	return m_inspector->get_thread(m_pid, true, true);

userspace/libsinsp/threadinfo.h

@@ -198,6 +198,14 @@ class SINSP_PUBLIC sinsp_threadinfo
 	*/
 	uint64_t get_fd_limit();
 
+	//
+	// Walk up the parent process heirarchy, calling the provided
+	// function for each node. If the function returns false, the
+	// traversal stops.
+	//
+	typedef std::function<bool (sinsp_threadinfo *)> visitor_func_t;
+	void traverse_parent_state(visitor_func_t &visitor);
+
 	//
 	// Core state
 	//
@@ -325,6 +333,7 @@ VISIBILITY_PRIVATE
 	uint16_t m_lastevent_type;
 	uint16_t m_lastevent_cpuid;
 	sinsp_evt::category m_lastevent_category;
+	bool m_parent_loop_detected;
 
 	friend class sinsp;
 	friend class sinsp_parser;