pkg/subsystem: add basic subsystem extraction code

For now, recognize just the vfs subsystem and support per-repro-call
subsystem inference.

2 files changed, 120 insertions, 0 deletions

diff --git a/pkg/subsystem/extract.go b/pkg/subsystem/extract.go
new file mode 100644
index 000000000..caf80636e
--- /dev/null
+++ b/pkg/subsystem/extract.go
@@ -0,0 +1,52 @@
+// Copyright 2022 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package subsystem
+
+import (
+	"regexp"
+
+	"github.com/google/syzkaller/prog"
+	"github.com/google/syzkaller/sys/targets"
+)
+
+type SubsystemExtractor struct {
+	CallToSubsystems func(call string) []string
+}
+
+// Crash contains the subset of Crash fields relevant for subsystem extraction.
+type Crash struct {
+	OS          string
+	GuiltyFiles []string
+	SyzRepro    string
+}
+
+func (se *SubsystemExtractor) Extract(crash *Crash) []string {
+	retMap := map[string]bool{}
+	// Currently we only have the dumbest possible implementation of subsystem detection.
+	if crash.OS == targets.Linux {
+		for _, guiltyPath := range crash.GuiltyFiles {
+			if vfsPathRegexp.MatchString(guiltyPath) {
+				retMap["vfs"] = true
+				break
+			}
+		}
+	}
+	if se.CallToSubsystems != nil {
+		callSet, _, _ := prog.CallSet([]byte(crash.SyzRepro))
+		for call := range callSet {
+			for _, subsystem := range se.CallToSubsystems(call) {
+				retMap[subsystem] = true
+			}
+		}
+	}
+	retSlice := []string{}
+	for name := range retMap {
+		retSlice = append(retSlice, name)
+	}
+	return retSlice
+}
+
+var (
+	vfsPathRegexp = regexp.MustCompile(`^fs/[^/]+\.c`)
+)
diff --git a/pkg/subsystem/extract_test.go b/pkg/subsystem/extract_test.go
new file mode 100644
index 000000000..936f4fa8e
--- /dev/null
+++ b/pkg/subsystem/extract_test.go
@@ -0,0 +1,68 @@
+// Copyright 2022 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package subsystem
+
+import (
+	"sort"
+	"testing"
+
+	"github.com/google/syzkaller/sys/targets"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSimpleLinuxExtract(t *testing.T) {
+	se := &SubsystemExtractor{}
+
+	ret := se.Extract(&Crash{
+		OS: targets.Linux,
+		GuiltyFiles: []string{
+			"fs/ext4/abc.c",
+		},
+	})
+	assert.Empty(t, ret, "the test should have found 0 subsystems")
+
+	ret = se.Extract(&Crash{
+		OS: targets.Linux,
+		GuiltyFiles: []string{
+			"fs/ext4/abc.c",
+			"fs/def.c",
+		},
+	})
+	assert.Exactly(t, ret, []string{"vfs"}, "the test should have only found vfs")
+}
+
+func TestProgCallRules(t *testing.T) {
+	se := &SubsystemExtractor{
+		CallToSubsystems: func(call string) []string {
+			ret := map[string][]string{
+				// Intentionally add some that are not present in the test below.
+				"test":               {"test"},
+				"syz_io_uring_setup": {"io_uring"},
+				"ioctl$TIOCSETD":     {"tty_ioctls", "tty"},
+				// Some calls are also omitted to verify that the code works fine this way.
+			}
+			return ret[call]
+		},
+	}
+
+	ret := se.Extract(&Crash{
+		OS: targets.Linux,
+		GuiltyFiles: []string{
+			"mm/page-writeback.c",
+		},
+		// nolint: lll
+		SyzRepro: `# https://syzkaller.appspot.com/bug?id=708185e841adf6ca28fc50b126fdf9825fd8ae43
+# See https://goo.gl/kgGztJ for information about syzkaller reproducers.
+#{"repeat":true,"procs":1,"slowdown":1,"sandbox":"","close_fds":false}
+r0 = syz_io_uring_setup(0x3ee4, &(0x7f0000000240), &(0x7f0000002000/0x2000)=nil, &(0x7f0000ffd000/0x3000)=nil, &(0x7f0000000100)=<r1=>0x0, &(0x7f0000000140)=<r2=>0x0)
+socket$inet_udplite(0x2, 0x2, 0x88)
+r3 = openat$ptmx(0xffffffffffffff9c, &(0x7f0000000040), 0x8a04, 0x0)
+syz_io_uring_submit(r1, r2, &(0x7f0000000000)=@IORING_OP_READ=@pass_buffer={0x16, 0x0, 0x0, @fd_index=0x5, 0x0, 0x0}, 0x0)
+ioctl$TIOCSETD(r3, 0x5423, &(0x7f0000000580)=0x3)
+io_uring_enter(r0, 0x2ff, 0x0, 0x0, 0x0, 0x0)`,
+	})
+	sort.Strings(ret)
+	assert.Exactlyf(t, ret, []string{"io_uring", "tty", "tty_ioctls"},
+		"invalid resulting subsystems: %s", ret)
+}