auditbeat/module/file_integrity: add support for selinux and posix_ac…

…l_access xattrs (#36310) (#36350)

(cherry picked from commit d771501)

Co-authored-by: Dan Kortschak <[email protected]>

CHANGELOG.next.asciidoc

@@ -149,6 +149,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 
 *Auditbeat*
 
+- Add support for `security.selinux` and `system.posix_acl_access` extended attributes to FIM. {issue}36265[36265] {pull}36310[36310]
 
 *Filebeat*
 

NOTICE.txt

@@ -21301,6 +21301,41 @@ OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
+--------------------------------------------------------------------------------
+Dependency : github.com/pkg/xattr
+Version: v0.4.9
+Licence type (autodetected): BSD-2-Clause
+--------------------------------------------------------------------------------
+
+Contents of probable licence file $GOMODCACHE/github.com/pkg/[email protected]/LICENSE:
+
+Copyright (c) 2012 Dave Cheney. All rights reserved.
+Copyright (c) 2014 Kuba Podgórski. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
 --------------------------------------------------------------------------------
 Dependency : github.com/pmezard/go-difflib
 Version: v1.0.0

auditbeat/module/file_integrity/event.go

@@ -23,12 +23,14 @@ import (
 	"crypto/sha1"
 	"crypto/sha256"
 	"crypto/sha512"
+	"encoding/binary"
 	"encoding/hex"
 	"fmt"
 	"hash"
 	"io"
 	"math"
 	"os"
+	"os/user"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -127,20 +129,22 @@ type Event struct {
 
 // Metadata contains file metadata.
 type Metadata struct {
-	Inode  uint64      `json:"inode"`
-	UID    uint32      `json:"uid"`
-	GID    uint32      `json:"gid"`
-	SID    string      `json:"sid"`
-	Owner  string      `json:"owner"`
-	Group  string      `json:"group"`
-	Size   uint64      `json:"size"`
-	MTime  time.Time   `json:"mtime"`  // Last modification time.
-	CTime  time.Time   `json:"ctime"`  // Last metadata change time.
-	Type   Type        `json:"type"`   // File type (dir, file, symlink).
-	Mode   os.FileMode `json:"mode"`   // Permissions
-	SetUID bool        `json:"setuid"` // setuid bit (POSIX only)
-	SetGID bool        `json:"setgid"` // setgid bit (POSIX only)
-	Origin []string    `json:"origin"` // External origin info for the file (MacOS only)
+	Inode          uint64      `json:"inode"`
+	UID            uint32      `json:"uid"`
+	GID            uint32      `json:"gid"`
+	SID            string      `json:"sid"`
+	Owner          string      `json:"owner"`
+	Group          string      `json:"group"`
+	Size           uint64      `json:"size"`
+	MTime          time.Time   `json:"mtime"`            // Last modification time.
+	CTime          time.Time   `json:"ctime"`            // Last metadata change time.
+	Type           Type        `json:"type"`             // File type (dir, file, symlink).
+	Mode           os.FileMode `json:"mode"`             // Permissions
+	SetUID         bool        `json:"setuid"`           // setuid bit (POSIX only)
+	SetGID         bool        `json:"setgid"`           // setgid bit (POSIX only)
+	Origin         []string    `json:"origin"`           // External origin info for the file (MacOS only)
+	SELinux        string      `json:"selinux"`          // security.selinux xattr value (Linux only)
+	POSIXACLAccess string      `json:"posix_acl_access"` // system.posix_acl_access xattr value (Linux only)
 }
 
 // NewEventFromFileInfo creates a new Event based on data from a os.FileInfo
@@ -319,6 +323,15 @@ func buildMetricbeatEvent(e *Event, existedBefore bool) mb.Event {
 		if len(info.Origin) > 0 {
 			file["origin"] = info.Origin
 		}
+		if info.SELinux != "" {
+			file["selinux"] = info.SELinux
+		}
+		if info.POSIXACLAccess != "" {
+			a, err := aclText([]byte(info.POSIXACLAccess))
+			if err == nil {
+				file["posix_acl_access"] = a
+			}
+		}
 	}
 
 	if len(e.Hashes) > 0 {
@@ -332,14 +345,14 @@ func buildMetricbeatEvent(e *Event, existedBefore bool) mb.Event {
 		file[k] = v
 	}
 
-	out.MetricSetFields.Put("event.kind", "event")              //nolint:errcheck // Will not error.
-	out.MetricSetFields.Put("event.category", []string{"file"}) //nolint:errcheck // Will not error.
+	out.MetricSetFields.Put("event.kind", "event")
+	out.MetricSetFields.Put("event.category", []string{"file"})
 	if e.Action > 0 {
 		actions := e.Action.InOrder(existedBefore, e.Info != nil)
-		out.MetricSetFields.Put("event.type", actions.ECSTypes())      //nolint:errcheck // Will not error.
-		out.MetricSetFields.Put("event.action", actions.StringArray()) //nolint:errcheck // Will not error.
+		out.MetricSetFields.Put("event.type", actions.ECSTypes())
+		out.MetricSetFields.Put("event.action", actions.StringArray())
 	} else {
-		out.MetricSetFields.Put("event.type", None.ECSTypes()) //nolint:errcheck // Will not error.
+		out.MetricSetFields.Put("event.type", None.ECSTypes())
 	}
 
 	if n := len(e.errors); n > 0 {
@@ -348,14 +361,82 @@ func buildMetricbeatEvent(e *Event, existedBefore bool) mb.Event {
 			errors[idx] = err.Error()
 		}
 		if n == 1 {
-			out.MetricSetFields.Put("error.message", errors[0]) //nolint:errcheck // Will not error.
+			out.MetricSetFields.Put("error.message", errors[0])
 		} else {
-			out.MetricSetFields.Put("error.message", errors) //nolint:errcheck // Will not error.
+			out.MetricSetFields.Put("error.message", errors)
 		}
 	}
 	return out
 }
 
+func aclText(b []byte) ([]string, error) {
+	if (len(b)-4)%8 != 0 {
+		return nil, fmt.Errorf("unexpected ACL length: %d", len(b))
+	}
+	b = b[4:] // The first four bytes is the version, discard it.
+	a := make([]string, 0, len(b)/8)
+	for len(b) != 0 {
+		tag := binary.LittleEndian.Uint16(b)
+		perm := binary.LittleEndian.Uint16(b[2:])
+		qual := binary.LittleEndian.Uint32(b[4:])
+		a = append(a, fmt.Sprintf("%s:%s:%s", tags[tag], qualString(qual, tag), modeString(perm)))
+		b = b[8:]
+	}
+	return a, nil
+}
+
+var tags = map[uint16]string{
+	0x00: "undefined",
+	0x01: "user",
+	0x02: "user",
+	0x04: "group",
+	0x08: "group",
+	0x10: "mask",
+	0x20: "other",
+}
+
+func qualString(qual uint32, tag uint16) string {
+	if qual == math.MaxUint32 {
+		// 0xffffffff is undefined ID, so return zero.
+		return ""
+	}
+	const (
+		tagUser  = 0x02
+		tagGroup = 0x08
+	)
+	id := strconv.Itoa(int(qual))
+	switch tag {
+	case tagUser:
+		u, err := user.LookupId(id)
+		if err == nil {
+			return u.Username
+		}
+	case tagGroup:
+		g, err := user.LookupGroupId(id)
+		if err == nil {
+			return g.Name
+		}
+	}
+	// Fallback to the numeric ID if we can't get a name
+	// or the tag is other than user/group.
+	return id
+}
+
+func modeString(perm uint16) string {
+	var buf [3]byte
+	w := 0
+	const rwx = "rwx"
+	for i, c := range rwx {
+		if perm&(1<<uint(len(rwx)-1-i)) != 0 {
+			buf[w] = byte(c)
+		} else {
+			buf[w] = '-'
+		}
+		w++
+	}
+	return string(buf[:w])
+}
+
 // diffEvents returns true if the file info differs between the old event and
 // the new event. Changes to the timestamp and action are ignored. If old
 // contains a superset of new's hashes then false is returned.
@@ -405,7 +486,8 @@ func diffEvents(old, new *Event) (Action, bool) {
 	if o, n := old.Info, new.Info; o != nil && n != nil {
 		// The owner and group names are ignored (they aren't persisted).
 		if o.Inode != n.Inode || o.UID != n.UID || o.GID != n.GID || o.SID != n.SID ||
-			o.Mode != n.Mode || o.Type != n.Type || o.SetUID != n.SetUID || o.SetGID != n.SetGID {
+			o.Mode != n.Mode || o.Type != n.Type || o.SetUID != n.SetUID || o.SetGID != n.SetGID ||
+			o.SELinux != n.SELinux || o.POSIXACLAccess != n.POSIXACLAccess {
 			result |= AttributesModified
 		}
 

auditbeat/module/file_integrity/event_test.go

@@ -19,12 +19,16 @@ package file_integrity
 
 import (
 	"bytes"
+	"encoding/base64"
 	"encoding/hex"
 	"fmt"
 	"io/ioutil"
 	"math"
 	"os"
+	"os/user"
+	"reflect"
 	"runtime"
+	"strings"
 	"testing"
 	"time"
 
@@ -553,3 +557,49 @@ func assertHasKey(t testing.TB, m mapstr.M, key string) bool {
 	}
 	return true
 }
+
+func TestACLText(t *testing.T) {
+	// The xattr package returns raw bytes, but command line tools such as getfattr
+	// return a base64-encoded format, so use that here to make test validation
+	// easier.
+	//
+	// Depending on the system we are running this test on, we may or may not
+	// have a username associated with the user's UID in the xattr string, so
+	// dynamically determine the username here.
+	tests := []struct {
+		encoded string
+		want    []string
+	}{
+		0: {
+			encoded: "0sAgAAAAEABgD/////AgAGAG8AAAAEAAQA/////xAABgD/////IAAEAP////8=",
+			want:    []string{"user::rw-", "user:" + userNameOrUID("111") + ":rw-", "group::r--", "mask::rw-", "other::r--"},
+		},
+		1: { // Encoded string from https://www.bityard.org/wiki/tech/os/linux/xattrs.
+			encoded: "0sAgAAAAEABgD/////AgAHAHwAAAAEAAQA/////xAABwD/////IAAEAP////8=",
+			want:    []string{"user::rw-", "user:" + userNameOrUID("124") + ":rwx", "group::r--", "mask::rwx", "other::r--"},
+		},
+	}
+	for i, test := range tests {
+		b, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(test.encoded, "0s"))
+		if err != nil {
+			t.Errorf("invalid test: unexpected base64 encoding error for test %d: %v", i, err)
+			continue
+		}
+		got, err := aclText(b)
+		if err != nil {
+			t.Errorf("unexpected error for test %d: %v", i, err)
+			continue
+		}
+		if !reflect.DeepEqual(got, test.want) {
+			t.Errorf("unexpected result for test %d:\ngot: %#v\nwant:%#v", i, got, test.want)
+		}
+	}
+}
+
+func userNameOrUID(uid string) string {
+	u, err := user.LookupId(uid)
+	if err != nil {
+		return uid
+	}
+	return u.Username
+}

auditbeat/module/file_integrity/fileinfo_posix.go

@@ -24,9 +24,11 @@ import (
 	"os"
 	"os/user"
 	"strconv"
+	"strings"
 	"syscall"
 
 	"github.com/joeshaw/multierror"
+	"github.com/pkg/xattr"
 )
 
 // NewMetadata returns a new Metadata object. If an error is returned it is
@@ -67,6 +69,17 @@ func NewMetadata(path string, info os.FileInfo) (*Metadata, error) {
 		fileInfo.Owner = owner.Username
 	}
 
+	getExtendedAttributes(path, map[string]*string{
+		"security.selinux":        &fileInfo.SELinux,
+		"system.posix_acl_access": &fileInfo.POSIXACLAccess,
+	})
+	// The selinux attr may be null terminated. It would be cheaper
+	// to use strings.TrimRight, but absent documentation saying
+	// that there is only ever a final null terminator, take the
+	// guaranteed correct path of terminating at the first found
+	// null byte.
+	fileInfo.SELinux, _, _ = strings.Cut(fileInfo.SELinux, "\x00")
+
 	group, err := user.LookupGroupId(strconv.Itoa(int(fileInfo.GID)))
 	if err != nil {
 		errs = append(errs, err)
@@ -78,3 +91,19 @@ func NewMetadata(path string, info os.FileInfo) (*Metadata, error) {
 	}
 	return fileInfo, errs.Err()
 }
+
+func getExtendedAttributes(path string, dst map[string]*string) {
+	f, err := os.Open(path)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	for n, d := range dst {
+		att, err := xattr.FGet(f, n)
+		if err != nil {
+			continue
+		}
+		*d = string(att)
+	}
+}