logger: introduce logger callbacks

loggerCallback() calls callbacks, log() and []logFnFilters(),
which can be set by the libbpfgo consumer via SetLoggerCbs().

This moves output filtering from C libbpf_print_fn() to
Go filterOutput() which can be set as one of the slice of filter funcs.

This also introduces LogWarnLevel, LogInfoLevel and LogDebugLevel
constants.

libbpfgo.h

@@ -15,46 +15,30 @@
 #include <bpf/bpf.h>
 #include <bpf/libbpf.h>
 
+extern void loggerCallback(enum libbpf_print_level level, char *output);
+
 int libbpf_print_fn(enum libbpf_print_level level, // libbpf print level
                     const char *format,            // format used for the msg
                     va_list args) {                // args used by format
 
-  if (level != LIBBPF_WARN)
-    return 0;
-
-  int ret;
-  char str[300];
+  int ret = 0;
+  char *out;
   va_list check;
 
+  out = (char *)calloc(1, 300);
+  if (!out)
+    return -ENOMEM;
+
   va_copy(check, args);
-  ret = vsnprintf(str, sizeof(str), format, check);
+  ret = vsnprintf(out, 300, format, check);
   va_end(check);
 
-  if (ret <= 0) {
-    goto done;
-  }
+  if (ret > 0)
+    loggerCallback(level, out);
 
-  // BUG: https:/github.com/aquasecurity/tracee/issues/1676
-  if (strstr(str, "Exclusivity flag on") != NULL) {
-    return 0;
-  }
-
-  // BUG: https://github.com/aquasecurity/tracee/issues/2446
-  if (strstr(str, "failed to create kprobe") != NULL) {
-    if (strstr(str, "trace_check_map_func_compatibility") != NULL)
-      return 0;
-  }
-
-  // AttachCgroupLegacy() will first try AttachCgroup() and it might fail. This
-  // is not an error and is the best way of probing for eBPF cgroup attachment
-  // link existence.
-  if (strstr(str, "cgroup") != NULL) {
-    if (strstr(str, "Invalid argument") != NULL)
-      return 0;
-  }
+  free(out);
 
-done:
-  return vfprintf(stderr, format, args);
+  return ret;
 }
 
 void set_print_fn() { libbpf_set_print(libbpf_print_fn); }

logger_cb.go

@@ -0,0 +1,157 @@
+package libbpfgo
+
+/*
+#include <bpf/libbpf.h>
+*/
+import "C"
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+	"strings"
+)
+
+// This callback definition needs to be in a different file from where it is declared in C
+// Otherwise, multiple definition compilation error will occur
+
+// loggerCallback is called by libbpf_print_fn() which in turn is called by libbpf
+//
+//export loggerCallback
+func loggerCallback(libbpfPrintLevel int, libbpfOutput *C.char) {
+	var (
+		level    int
+		goOutput string
+	)
+
+	goOutput = C.GoString(libbpfOutput)
+	goOutput = strings.TrimSuffix(goOutput, "\n")
+
+	for _, fnFilterOut := range logFnFilters {
+		if fnFilterOut != nil {
+			if fnFilterOut(libbpfPrintLevel, goOutput) {
+				return
+			}
+		}
+	}
+
+	log(level, goOutput)
+}
+
+const (
+	LogWarnLevel  = int(C.LIBBPF_WARN)
+	LogInfoLevel  = int(C.LIBBPF_INFO)
+	LogDebugLevel = int(C.LIBBPF_DEBUG)
+)
+
+var log = logFallback
+var logFnFilters = []func(libLevel int, msg string) bool{
+	LogFilterLevel,
+	LogFilterOutput,
+}
+
+// SetLoggerCbs receives a function to be used to log libbpf outputs and
+// a list of functions to filter this output out
+// If fnLog is nil, logFallback will continue to be used
+// If fnFilters is nil, logFnFilters will continue to be used
+func SetLoggerCbs(
+	fnLog func(level int, msg string, keyValues ...interface{}), // log callback
+	fnFilters []func(libLevel int, msg string) bool, // Filter out callbacks
+) {
+	if fnLog != nil {
+		log = fnLog
+	}
+	if fnFilters != nil {
+		logFnFilters = fnFilters
+	}
+}
+
+// logFallback:
+// - level is ignored in this stage
+// - type coercion only takes care of string types
+// - keyValues is not required to contain pairs
+// - outputs all to stderr
+func logFallback(level int, msg string, keyValues ...interface{}) {
+	var (
+		args   = make([]string, 0)
+		outMsg = msg
+	)
+
+	for _, v := range keyValues {
+		if s, ok := v.(string); ok {
+			outMsg += " [%s]"
+			args = append(args, s)
+		}
+	}
+
+	outMsg += "\n"
+	if len(keyValues) > 0 {
+		fmt.Fprintf(os.Stderr, outMsg, args)
+	} else {
+		fmt.Fprint(os.Stderr, outMsg)
+	}
+}
+
+// LogFilterLevel filters by checking its print level
+// In case the consumer defines its own filters functions via SetLoggerCbs, this can also be passed
+func LogFilterLevel(libbpfPrintLevel int, output string) bool {
+	return libbpfPrintLevel != LogWarnLevel
+}
+
+// LogFilterOutput filters out some errors by using regex
+// In case the consumer defines its own filters functions via SetLoggerCbs, this can also be passed
+func LogFilterOutput(libbpfPrintLevel int, output string) bool {
+	var (
+		matched bool
+		err     error
+	)
+
+	// BUG: https:/github.com/aquasecurity/tracee/issues/1676
+
+	// triggered by: libbpf/src/nlattr.c->libbpf_nla_dump_errormsg()
+	// "libbpf: Kernel error message: %s\n"
+	// 1. %s = "Exclusivity flag on"
+
+	matched, err = regexp.MatchString(`libbpf:.*Kernel error message:.*Exclusivity flag on`, output)
+	if err != nil {
+		log(LogDebugLevel, "Filtering libbpf print output", "error", err)
+	} else if matched {
+		return true
+	}
+
+	// BUG: https://github.com/aquasecurity/tracee/issues/2446
+
+	// triggered by: libbpf/src/libbpf.c->bpf_program__attach_kprobe_opts()
+	// "libbpf: prog '%s': failed to create %s '%s+0x%zx' perf event: %s\n"
+	// 1. %s = trace_check_map_func_compatibility
+	// 2. %s = kretprobe or kprobe
+	// 3. %s = check_map_func_compatibility (function name)
+	// 4. %x = offset (ignored in this check)
+	// 5. %s = No such file or directory
+
+	matched, err = regexp.MatchString(`libbpf:.*prog 'trace_check_map_func_compatibility'.*failed to create kprobe.*perf event: No such file or directory`, output)
+	if err != nil {
+		log(LogDebugLevel, "Filtering libbpf print output", "error", err)
+	} else if matched {
+		return true
+	}
+
+	// AttachCgroupLegacy() will first try AttachCgroup() and it might fail. This
+	// is not an error and is the best way of probing for eBPF cgroup attachment
+	// link existence.
+
+	// triggered by: libbpf/src/libbpf.c->bpf_program__attach_fd()
+	// "libbpf: prog '%s': failed to attach to %s: %s\n"
+	// 1. %s = cgroup_skb_ingress or cgroup_skb_egress
+	// 2. %s = cgroup
+	// 3. %s = Invalid argument
+
+	matched, err = regexp.MatchString(`libbpf:.*prog 'cgroup_skb_ingress|cgroup_skb_egress'.*failed to attach to cgroup.*Invalid argument`, output)
+	if err != nil {
+		log(LogDebugLevel, "Filtering libbpf print output", "error", err)
+	} else if matched {
+		return true
+	}
+
+	return false
+}