fix(elf): avoid a panic on a truncated dynamic section (#5321)

Signed-off-by: somaz <genius5711@gmail.com>

syft/file/cataloger/executable/elf.go

@@ -156,32 +156,12 @@ func hasElfDynFlag1(f *elf.File, flag elf.DynFlag1) bool {
 }
 
 func hasElfDynTag(f *elf.File, tag elf.DynTag) bool {
-	// source https://github.com/golang/go/blob/9b4b3e5acca2dabe107fa2c3ed963097d78a4562/src/cmd/cgo/internal/testshared/shared_test.go#L280
+	vals, err := f.DynValue(tag)
-
-	ds := f.SectionByType(elf.SHT_DYNAMIC)
-	if ds == nil {
-		return false
-	}
-	d, err := ds.Data()
 	if err != nil {
+		log.WithFields("error", err).Trace("unable to read dynamic section from elf file")
 		return false
 	}
-
+	return len(vals) > 0
-	for len(d) > 0 {
-		var t elf.DynTag
-		switch f.Class {
-		case elf.ELFCLASS32:
-			t = elf.DynTag(f.ByteOrder.Uint32(d[0:4]))
-			d = d[8:]
-		case elf.ELFCLASS64:
-			t = elf.DynTag(f.ByteOrder.Uint64(d[0:8]))
-			d = d[16:]
-		}
-		if t == tag {
-			return true
-		}
-	}
-	return false
 }
 
 func isELFPIE(f *elf.File) bool {

syft/file/cataloger/executable/elf_test.go

@@ -1,7 +1,9 @@
 package executable
 
 import (
+	"bytes"
 	"debug/elf"
+	"encoding/binary"
 	"os"
 	"path/filepath"
 	"testing"
@@ -226,3 +228,89 @@ func Test_elfHasExports(t *testing.T) {
 		})
 	}
 }
+
+func Test_hasElfDynTag(t *testing.T) {
+	dynEntry := func(class elf.Class, tag elf.DynTag) []byte {
+		if class == elf.ELFCLASS32 {
+			return binary.LittleEndian.AppendUint32(binary.LittleEndian.AppendUint32(nil, uint32(tag)), 0)
+		}
+		return binary.LittleEndian.AppendUint64(binary.LittleEndian.AppendUint64(nil, uint64(tag)), 0)
+	}
+
+	tests := []struct {
+		name    string
+		class   elf.Class
+		dynamic []byte
+		want    bool
+	}{
+		{
+			name:    "32-bit tag present",
+			class:   elf.ELFCLASS32,
+			dynamic: dynEntry(elf.ELFCLASS32, elf.DT_BIND_NOW),
+			want:    true,
+		},
+		{
+			name:    "64-bit tag present",
+			class:   elf.ELFCLASS64,
+			dynamic: dynEntry(elf.ELFCLASS64, elf.DT_BIND_NOW),
+			want:    true,
+		},
+		{
+			name:    "64-bit tag absent",
+			class:   elf.ELFCLASS64,
+			dynamic: dynEntry(elf.ELFCLASS64, elf.DT_NULL),
+			want:    false,
+		},
+		{
+			name:    "32-bit truncated dynamic section",
+			class:   elf.ELFCLASS32,
+			dynamic: dynEntry(elf.ELFCLASS32, elf.DT_BIND_NOW)[:4],
+			want:    false,
+		},
+		{
+			name:    "64-bit truncated dynamic section",
+			class:   elf.ELFCLASS64,
+			dynamic: dynEntry(elf.ELFCLASS64, elf.DT_BIND_NOW)[:12],
+			want:    false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			f, err := elf.NewFile(bytes.NewReader(elfWithDynamicSection(t, tt.class, tt.dynamic)))
+			require.NoError(t, err)
+			assert.Equal(t, tt.want, hasElfDynTag(f, elf.DT_BIND_NOW))
+		})
+	}
+}
+
+// elfWithDynamicSection builds a little-endian ELF holding only a null section and a SHT_DYNAMIC section.
+func elfWithDynamicSection(t *testing.T, class elf.Class, dynamic []byte) []byte {
+	t.Helper()
+	ident := [elf.EI_NIDENT]byte{0x7f, 'E', 'L', 'F', byte(class), byte(elf.ELFDATA2LSB), byte(elf.EV_CURRENT)}
+	var buf bytes.Buffer
+	write := func(v any) {
+		require.NoError(t, binary.Write(&buf, binary.LittleEndian, v))
+	}
+
+	if class == elf.ELFCLASS32 {
+		ehsize, shentsize := binary.Size(elf.Header32{}), binary.Size(elf.Section32{})
+		dataOff := ehsize + 2*shentsize
+		write(elf.Header32{
+			Ident: ident, Type: uint16(elf.ET_DYN), Machine: uint16(elf.EM_386), Version: uint32(elf.EV_CURRENT),
+			Shoff: uint32(ehsize), Ehsize: uint16(ehsize), Shentsize: uint16(shentsize), Shnum: 2,
+		})
+		write(elf.Section32{})
+		write(elf.Section32{Type: uint32(elf.SHT_DYNAMIC), Off: uint32(dataOff), Size: uint32(len(dynamic)), Addralign: 1})
+	} else {
+		ehsize, shentsize := binary.Size(elf.Header64{}), binary.Size(elf.Section64{})
+		dataOff := ehsize + 2*shentsize
+		write(elf.Header64{
+			Ident: ident, Type: uint16(elf.ET_DYN), Machine: uint16(elf.EM_X86_64), Version: uint32(elf.EV_CURRENT),
+			Shoff: uint64(ehsize), Ehsize: uint16(ehsize), Shentsize: uint16(shentsize), Shnum: 2,
+		})
+		write(elf.Section64{})
+		write(elf.Section64{Type: uint32(elf.SHT_DYNAMIC), Off: uint64(dataOff), Size: uint64(len(dynamic)), Addralign: 1})
+	}
+	buf.Write(dynamic)
+	return buf.Bytes()
+}