Document and improve permission checks when running socket metricset …

…from Docker (elastic#12039)

Update instructions for system/socket metricset on Docker. And base
permission checks on capabilities rather than on the effective uid.
Running a process as root doesn't mean that it has all privileges,
specially when run as container.

CHANGELOG.next.asciidoc

@@ -111,6 +111,8 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Change diskio metrics retrieval method (only for Windows) from wmi query to DeviceIOControl function using the IOCTL_DISK_PERFORMANCE control code {pull}11635[11635]
 - Call GetMetricData api per region instead of per instance. {issue}11820[11820] {pull}11882[11882]
 - Update documentation with cloudwatch:ListMetrics permission. {pull}11987[11987]
+- Check permissions in system socket metricset based on capabilities. {pull}12039[12039]
+- Get process information from sockets owned by current user when system socket metricset is run without privileges. {pull}12039[12039]
 - Avoid generating hints-based configuration with empty hosts when no exposed port is suitable for the hosts hint. {issue}8264[8264] {pull}12086[12086]
 - Fixed a socket leak in the postgresql module under Windows when SSL is disabled on the server. {pull}11393[11393]
 

libbeat/common/capabilities_linux.go

@@ -0,0 +1,62 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// +build linux
+
+package common
+
+import (
+	"github.com/pkg/errors"
+
+	"github.com/elastic/go-sysinfo"
+	"github.com/elastic/go-sysinfo/types"
+)
+
+// Capabilities contains the capability sets of a process
+type Capabilities types.CapabilityInfo
+
+// Check performs a permission check for a given capabilities set
+func (c Capabilities) Check(set []string) bool {
+	for _, capability := range set {
+		found := false
+		for _, effective := range c.Effective {
+			if capability == effective {
+				found = true
+				break
+			}
+		}
+		if !found {
+			return false
+		}
+	}
+	return true
+}
+
+// GetCapabilities gets the capabilities of this process
+func GetCapabilities() (Capabilities, error) {
+	p, err := sysinfo.Self()
+	if err != nil {
+		return Capabilities{}, errors.Wrap(err, "failed to read self process information")
+	}
+
+	if c, ok := p.(types.Capabilities); ok {
+		capabilities, err := c.Capabilities()
+		return Capabilities(*capabilities), errors.Wrap(err, "failed to read process capabilities")
+	}
+
+	return Capabilities{}, errors.New("capabilities not available")
+}

metricbeat/docs/running-on-docker.asciidoc

@@ -46,7 +46,20 @@ NOTE: The special filesystems +/proc+ and +/sys+ are only available if the
 host system is running Linux. Attempts to bind-mount these filesystems will
 fail on Windows and MacOS.
 
+
+If the <<metricbeat-metricset-system-socket,system socket metricset>>
+is being used on Linux, more privileges will need to be granted to Metricbeat.
+This metricset reads files from `/proc` that are an interface to internal
+objects owned by other users. The capabilities needed to read all these files
+(`sys_ptrace` and `dac_read_search`) are disabled by default on Docker. To
+grant these permissions these flags are needed too:
+
+["source","sh",subs="attributes"]
+----
+--user root --cap-add sys_ptrace --cap-add dac_read_search
+----
 [float]
+
 [[monitoring-service]]
 ==== Monitor a service in another container
 

metricbeat/helper/socket/ptable.go

@@ -15,12 +15,15 @@
 // specific language governing permissions and limitations
 // under the License.
 
+// +build !windows
+
 package socket
 
 import (
 	"os"
 	"strconv"
 	"strings"
+	"syscall"
 
 	"github.com/joeshaw/multierror"
 	"github.com/prometheus/procfs"
@@ -39,10 +42,10 @@ type Proc struct {
 
 // ProcTable contains all of the active processes (if the current user is root).
 type ProcTable struct {
-	fs     procfs.FS
-	procs  map[int]*Proc
-	inodes map[uint32]*Proc
-	euid   int
+	fs         procfs.FS
+	procs      map[int]*Proc
+	inodes     map[uint32]*Proc
+	privileged bool
 }
 
 // NewProcTable returns a new ProcTable that reads data from the /proc
@@ -58,29 +61,30 @@ func NewProcTable(mountpoint string) (*ProcTable, error) {
 		return nil, err
 	}
 
-	p := &ProcTable{fs: fs, euid: os.Geteuid()}
+	privileged, err := isPrivileged()
+	if err != nil {
+		return nil, err
+	}
+
+	p := &ProcTable{fs: fs, privileged: privileged}
 	p.Refresh()
 	return p, nil
 }
 
+// Privileged returns true if the process has enough permissions to read
+// sockets of all users
+func (t *ProcTable) Privileged() bool {
+	return t.privileged
+}
+
 // Refresh updates the process table with new processes and removes processes
 // that have exited. It collects the PID, command, and socket inode information.
 // If running as non-root, only information from the current process will be
 // collected.
 func (t *ProcTable) Refresh() error {
-	var err error
-	var procs []procfs.Proc
-	if t.euid == 0 {
-		procs, err = t.fs.AllProcs()
-		if err != nil {
-			return err
-		}
-	} else {
-		proc, err := t.fs.Self()
-		if err != nil {
-			return err
-		}
-		procs = append(procs, proc)
+	procs, err := t.accessibleProcs()
+	if err != nil {
+		return err
 	}
 
 	var errs multierror.Errors
@@ -124,6 +128,35 @@ func (t *ProcTable) Refresh() error {
 	return errs.Err()
 }
 
+func (t *ProcTable) accessibleProcs() ([]procfs.Proc, error) {
+	procs, err := t.fs.AllProcs()
+	if err != nil {
+		return nil, err
+	}
+	if t.privileged {
+		return procs, nil
+	}
+
+	// Filter out not owned processes
+	k := 0
+	euid := uint32(os.Geteuid())
+	for i := 0; i < len(procs); i++ {
+		p := t.fs.Path(strconv.Itoa(procs[i].PID))
+		info, err := os.Stat(p)
+		if err != nil {
+			continue
+		}
+		stat, ok := info.Sys().(*syscall.Stat_t)
+		if !ok || stat.Uid != euid {
+			continue
+		}
+		procs[k] = procs[i]
+		k++
+	}
+
+	return procs[:k], nil
+}
+
 func socketInodes(p *procfs.Proc) ([]uint32, error) {
 	fds, err := p.FileDescriptorTargets()
 	if err != nil {

metricbeat/helper/socket/ptable_linux.go

@@ -0,0 +1,36 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// +build linux
+
+package socket
+
+import (
+	"github.com/elastic/beats/libbeat/common"
+)
+
+var requiredCapabilities = []string{"sys_ptrace", "dac_read_search"}
+
+// isPrivileged checks if this process has privileges to read sockets
+// of all users
+func isPrivileged() (bool, error) {
+	capabilities, err := common.GetCapabilities()
+	if err != nil {
+		return false, err
+	}
+	return capabilities.Check(requiredCapabilities), nil
+}

metricbeat/helper/socket/ptable_other.go

@@ -0,0 +1,30 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// +build !linux,!windows
+
+package socket
+
+import (
+	"os"
+)
+
+// isPrivileged checks if this process has privileges to read sockets
+// of all users
+func isPrivileged() (bool, error) {
+	return os.Geteuid() == 0, nil
+}

metricbeat/module/system/socket/_meta/docs.asciidoc

@@ -19,9 +19,11 @@ metricbeat.modules:
 <1> You can configure the `socket` metricset separately to specify a different
 `period` value than the other metricsets.
 
-The metricset reports the process that has the socket open. In order to provide
-this information, Metricbeat must be running as root. Root access is also
-required to read the file descriptor information of other processes.
+The metricset reports the process that has the socket open. To provide this
+information on Linux for all processes, Metricbeat must be run with
+`sys_ptrace` and `dac_read_search` capabilities. These permissions are usually
+granted when running as root, but they can and may need to be explictly added
+when running Metricbeat inside a container.
 
 [float]
 === Configuration

metricbeat/module/system/socket/socket.go

@@ -77,9 +77,9 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 	if err != nil {
 		return nil, err
 	}
-	if os.Geteuid() != 0 {
-		logp.Info("socket process info will only be available for " +
-			"metricbeat because the process is running as a non-root user")
+	if !ptable.Privileged() {
+		logp.Info("socket process info will only be available for processes owned by the %v user "+
+			"because this Beat is not running with enough privileges", os.Geteuid())
 	}
 
 	m := &MetricSet{
@@ -212,7 +212,7 @@ func (m *MetricSet) enrichConnectionData(c *connection) {
 		c.Command = proc.Command
 		c.CmdLine = proc.CmdLine
 		c.Args = proc.Args
-	} else if m.euid == 0 {
+	} else if m.ptable.Privileged() {
 		if c.Inode == 0 {
 			c.ProcessError = fmt.Errorf("process has exited. inode=%v, tcp_state=%v",
 				c.Inode, c.State)