x-pack/auditbeat/module/socket/guess: fix creds trigger for newer ker…

…nels

In kernel commit 981ee95c (into v6.3) calls to access_override_creds
were gated behind a test for the requirement for the call. This change
results in non-execution of prepare_creds and so failure of the guess.

An alternative has been identified that does not exhibit this behaviour,
mq_open. So replace the sys_access trigger with sys_mq_open.

CHANGELOG.next.asciidoc

@@ -65,6 +65,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 
 *Auditbeat*
 
+- Fix guess trigger for system/socket creds on newer kernels. {issue}36905[36905] {pull}37136[37136]
 
 *Filebeat*
 

x-pack/auditbeat/module/system/socket/guess/creds.go

@@ -19,6 +19,17 @@ import (
 	"github.com/elastic/elastic-agent-libs/mapstr"
 )
 
+/*
+struct mq_attr {
+	long mq_flags;
+	long mq_maxmsg;
+	long mq_msgsize;
+	long mq_curmsgs;
+	long __reserved[4];
+};
+*/
+import "C"
+
 /*
 	creds guess discovers the offsets of (E)UID/(E)GID fields within a
     struct cred (defined in {linux}/include/linux.cred.h):
@@ -138,13 +149,26 @@ func (g *guessStructCreds) Extract(ev interface{}) (mapstr.M, bool) {
 	}, true
 }
 
-// Trigger invokes the SYS_ACCESS syscall:
-//
-//	int access(const char *pathname, int mode);
+// Trigger invokes the SYS_MQ_OPEN syscall:
 //
-// The function call will return an error due to path being NULL, but it will
-// have invoked prepare_creds before argument validation.
+//	int mq_open(const char *name, int oflag, mode_t mode, struct mq_attr *attr);
 func (g *guessStructCreds) Trigger() error {
-	syscall.Syscall(unix.SYS_ACCESS, 0, 0, 0)
-	return nil
+	name, err := unix.BytePtrFromString("/omg")
+	if err != nil {
+		return err
+	}
+	attr := C.struct_mq_attr{
+		mq_maxmsg:  1,
+		mq_msgsize: 8,
+	}
+	mqd, _, err := syscall.Syscall6(unix.SYS_MQ_OPEN,
+		uintptr(unsafe.Pointer(name)),
+		uintptr(os.O_CREATE|os.O_RDWR),
+		0o644,
+		uintptr(unsafe.Pointer(&attr)),
+		0, 0)
+	if err != syscall.Errno(0) {
+		return err
+	}
+	return unix.Close(int(mqd))
 }