extract dep info from wasm modules (#6)

Author: Tom Fay

.gitignore

@@ -15,3 +15,4 @@
 # vendor/
 
 crate_with_features_bin
+wasm_crate.wasm

rustaudit.go

@@ -6,6 +6,7 @@ import (
 	"debug/elf"
 	"debug/macho"
 	"debug/pe"
+	"encoding/binary"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -60,6 +61,11 @@ var (
 	machoHeader             = []byte("\xFE\xED\xFA")
 	machoHeaderLittleEndian = []byte("\xFA\xED\xFE")
 	machoUniversalHeader    = []byte("\xCA\xFE\xBA\xBE")
+	// https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#binary-magic
+	wasmHeader = []byte("\x00asm\x01\x00\x00\x00")
+
+	cargoAuditableSectionName       = ".dep-v0"
+	cargoAuditableLegacySectionName = ".rust-deps-v0"
 )
 
 func GetDependencyInfo(r io.ReaderAt) (VersionInfo, error) {
@@ -90,6 +96,8 @@ func GetDependencyInfo(r io.ReaderAt) (VersionInfo, error) {
 			return VersionInfo{}, ErrUnknownFileFormat
 		}
 		x = &machoExe{f}
+	case bytes.HasPrefix(header, wasmHeader):
+		x = &wasmReader{r}
 	default:
 		return VersionInfo{}, ErrUnknownFileFormat
 	}
@@ -135,13 +143,13 @@ type elfExe struct {
 func (x *elfExe) ReadRustDepSection() ([]byte, error) {
 	// Try .dep-v0 first, falling back to .rust-deps-v0 as used in
 	// in rust-audit 0.1.0
-	depInfo := x.f.Section(".dep-v0")
+	depInfo := x.f.Section(cargoAuditableSectionName)
 
 	if depInfo != nil {
 		return depInfo.Data()
 	}
 
-	depInfo = x.f.Section(".rust-deps-v0")
+	depInfo = x.f.Section(cargoAuditableLegacySectionName)
 
 	if depInfo == nil {
 		return nil, ErrNoRustDepInfo
@@ -157,7 +165,7 @@ type peExe struct {
 func (x *peExe) ReadRustDepSection() ([]byte, error) {
 	// Try .dep-v0 first, falling back to rdep-v0 as used in
 	// in rust-audit 0.1.0
-	depInfo := x.f.Section(".dep-v0")
+	depInfo := x.f.Section(cargoAuditableSectionName)
 
 	if depInfo != nil {
 		return depInfo.Data()
@@ -179,7 +187,7 @@ type machoExe struct {
 func (x *machoExe) ReadRustDepSection() ([]byte, error) {
 	// Try .dep-v0 first, falling back to rust-deps-v0 as used in
 	// in rust-audit 0.1.0
-	depInfo := x.f.Section(".dep-v0")
+	depInfo := x.f.Section(cargoAuditableSectionName)
 
 	if depInfo != nil {
 		return depInfo.Data()
@@ -193,3 +201,98 @@ func (x *machoExe) ReadRustDepSection() ([]byte, error) {
 
 	return depInfo.Data()
 }
+
+type wasmReader struct {
+	r io.ReaderAt
+}
+
+func (x *wasmReader) ReadRustDepSection() ([]byte, error) {
+	r := x.r
+	var offset int64 = 0
+
+	// Check the preamble (magic number and version)
+	buf := make([]byte, 8)
+	_, err := r.ReadAt(buf, offset)
+	offset += 8
+	if err != nil || !bytes.Equal(buf, wasmHeader) {
+		return nil, ErrUnknownFileFormat
+	}
+
+	// https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#custom-section%E2%91%A0
+	// Look through the sections until we find a custom .dep-v0 section or EOF
+	for {
+		// Read single byte section ID
+		sectionId := make([]byte, 1)
+		_, err = r.ReadAt(sectionId, offset)
+		offset += 1
+		if err == io.EOF {
+			return nil, ErrNoRustDepInfo
+		} else if err != nil {
+			return nil, ErrUnknownFileFormat
+		}
+
+		// Read section size
+		buf = make([]byte, 4)
+		_, err = r.ReadAt(buf, offset)
+		if err != nil {
+			return nil, ErrUnknownFileFormat
+		}
+		sectionSize, n, err := readUint32(buf)
+		if err != nil {
+			return nil, ErrUnknownFileFormat
+		}
+		offset += n
+		nextSection := offset + int64(sectionSize)
+
+		// Custom sections have a zero section ID
+		if sectionId[0] != 0 {
+			offset = nextSection
+			continue
+		}
+
+		// The custom section has a variable length name
+		// followed by the data
+		_, err = r.ReadAt(buf, offset)
+		if err != nil {
+			return nil, ErrUnknownFileFormat
+		}
+		nameSize, n, err := readUint32(buf)
+		if err != nil {
+			return nil, ErrUnknownFileFormat
+		}
+		offset += n
+
+		// Read section name
+		name := make([]byte, nameSize)
+		_, err = r.ReadAt(name, offset)
+		if err != nil {
+			return nil, ErrUnknownFileFormat
+		}
+		offset += int64(nameSize)
+
+		// Is this our custom section?
+		if string(name) != cargoAuditableSectionName {
+			offset = nextSection
+			continue
+		}
+
+		// Read audit data
+		data := make([]byte, nextSection-offset)
+		_, err = r.ReadAt(data, offset)
+		if err != nil {
+			return nil, ErrUnknownFileFormat
+		}
+		return data, nil
+
+	}
+}
+
+// wrap binary.Uvarint to return uint32, checking for overflow
+// https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#integers%E2%91%A4
+func readUint32(buf []byte) (uint32, int64, error) {
+	v, n := binary.Uvarint(buf)
+	if n <= 0 || v > uint64(^uint32(0)) {
+		return 0, 0, fmt.Errorf("overflow decoding uint32")
+	}
+	return uint32(v), int64(n), nil
+}

rustaudit_test.go

@@ -1,6 +1,7 @@
 package rustaudit
 
 import (
+	"bytes"
 	"log"
 	"os"
 	"testing"
@@ -22,3 +23,36 @@ func TestLinuxRustDependencies(t *testing.T) {
 	assert.Equal(t, Package{Name: "crate_with_features", Version: "0.1.0", Source: "local", Kind: "runtime", Dependencies: []uint{1}, Root: true}, versionInfo.Packages[0])
 	assert.Equal(t, false, versionInfo.Packages[1].Root)
 }
+
+func TestWasmRustDependencies(t *testing.T) {
+	// Generate this with `DOCKER_BUILDKIT=1 docker build -f test/Dockerfile -o . .`
+	r, err := os.Open("wasm_crate.wasm")
+	if err != nil {
+		log.Fatal(err)
+	}
+	versionInfo, err := GetDependencyInfo(r)
+	if err != nil {
+		log.Fatal(err)
+	}
+	assert.Equal(t, 18, len(versionInfo.Packages))
+	assert.Equal(t, Package{Name: "bumpalo", Version: "3.16.0", Source: "crates.io", Kind: "runtime", Dependencies: nil, Root: false}, versionInfo.Packages[0])
+	assert.Equal(t, false, versionInfo.Packages[1].Root)
+}
+
+func FuzzWasm(f *testing.F) {
+	// Use the test fixture as a seed
+	data, err := os.ReadFile("wasm_crate.wasm")
+	if err != nil {
+		log.Fatal(err)
+	}
+	f.Add(data)
+	f.Fuzz(func(t *testing.T, input []byte) {
+		r := bytes.NewReader(input)
+		w := wasmReader{r}
+
+		_, err := w.ReadRustDepSection()
+		if err != ErrNoRustDepInfo && err != ErrUnknownFileFormat && err != nil {
+			t.Errorf("Unexpected error: %v", err)
+		}
+	})
+}

test/Dockerfile

@@ -1,10 +1,14 @@
-FROM rust:1.62.1-bullseye as builder
+FROM rust:1.79.0-bullseye as builder
 RUN git clone https://github.com/rust-secure-code/cargo-auditable.git
 WORKDIR /cargo-auditable/cargo-auditable
 RUN cargo build
+RUN rustup target add wasm32-unknown-unknown
+WORKDIR /cargo-auditable/cargo-auditable/tests/fixtures/wasm_crate
+RUN /cargo-auditable/target/debug/cargo-auditable auditable build --target wasm32-unknown-unknown
 WORKDIR /cargo-auditable/cargo-auditable/tests/fixtures/workspace
 RUN /cargo-auditable/target/debug/cargo-auditable auditable build
 FROM scratch
 COPY --from=builder \
+  /cargo-auditable/cargo-auditable/tests/fixtures/wasm_crate/target/wasm32-unknown-unknown/debug/wasm_crate.wasm \
   /cargo-auditable/cargo-auditable/tests/fixtures/workspace/target/debug/crate_with_features_bin \
-  /crate_with_features_bin
+  /