fix(dotnet): bound the bundle signature search by the file, not the headers

The single-file bundle marker search sized its buffer from `calculatePEEndOffset` /
`calculateELFEndOffset`, both of which sum user-controlled header fields. A tiny file
declaring 4GB sections drove an 8.6GB allocation, and on the ELF side the sum could
overflow negative and panic in `make`.

The search now clamps its window to the real file length before sizing anything. The PE
and ELF paths had grown two copies of the same find-and-read sequence, so they collapse
into one `bundle.ExtractDepsJSON`, which lets the signature search and the header reader
both go unexported.

Also guards `read7BitEncodedInt` against returning a negative length, which on a 32-bit
`int` would seek a manifest walk backwards and re-read the same bytes per declared file.

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

syft/pkg/cataloger/internal/dotnet/bundle/bundle.go

@@ -1,6 +1,7 @@
 package bundle
 
 import (
+	"bytes"
 	"encoding/binary"
 	"errors"
 	"fmt"
@@ -15,6 +16,54 @@ var dotNetBundleSignature = []byte{
 	0xee, 0x3b, 0x2d, 0xce, 0x24, 0xb3, 0x6a, 0xae,
 }
 
+// ExtractDepsJSON returns the deps.json embedded in the .NET single-file bundle in r, or "" if r carries no
+// bundle marker.
+//
+// searchLimit is where the caller's format parsing says the executable structure ends, which is as far into
+// the file as the marker can be. It comes from user-controlled header fields, so it may describe far more
+// than the file holds or overflow negative; it is clamped to the real file length before anything is sized
+// from it. A non-positive limit reads nothing.
+func ExtractDepsJSON(r io.ReadSeeker, searchLimit int64) (string, error) {
+	headerOffset, err := findSignatureOffset(r, searchLimit)
+	if err != nil || headerOffset == 0 {
+		return "", err
+	}
+
+	return readDepsJSONFromBundleHeader(r, headerOffset)
+}
+
+// findSignatureOffset searches the start of r for the .NET single-file bundle signature and returns the
+// bundle header offset stored in the 8 bytes immediately before it, or 0 if the signature is not found.
+func findSignatureOffset(r io.ReadSeeker, searchLimit int64) (int64, error) {
+	if searchLimit <= 0 {
+		return 0, nil
+	}
+
+	end, err := r.Seek(0, io.SeekEnd)
+	if err != nil {
+		return 0, err
+	}
+
+	if _, err := r.Seek(0, io.SeekStart); err != nil {
+		return 0, err
+	}
+
+	// this scans a whole executable, routinely over 100MB for a single-file bundle, so the buffer is sized
+	// exactly once. An append-growing read holds both arrays at its final growth and would cost well over
+	// twice the file's own size for the same result.
+	searchData := make([]byte, min(searchLimit, end))
+	if _, err := io.ReadFull(r, searchData); err != nil {
+		return 0, err
+	}
+
+	idx := bytes.Index(searchData, dotNetBundleSignature)
+	if idx == -1 || idx < 8 {
+		return 0, nil
+	}
+
+	return int64(binary.LittleEndian.Uint64(searchData[idx-8 : idx])), nil
+}
+
 // dotNetBundleHeader represents the fixed portion of the bundle header (version 1+)
 type dotNetBundleHeader struct {
 	MajorVersion     uint32
@@ -44,7 +93,7 @@ const (
 )
 
 // ReadDepsJSONFromBundleHeader parses the bundle header at the given offset and extracts deps.json content.
-func ReadDepsJSONFromBundleHeader(r io.ReadSeeker, headerOffset int64) (string, error) {
+func readDepsJSONFromBundleHeader(r io.ReadSeeker, headerOffset int64) (string, error) {
 	if _, err := r.Seek(headerOffset, io.SeekStart); err != nil {
 		return "", err
 	}
@@ -103,6 +152,13 @@ func read7BitEncodedInt(r io.Reader) (int, error) {
 			return 0, errors.New("invalid 7-bit encoded int")
 		}
 	}
+
+	// the shift above can carry past int32 where int is 32 bits, and a negative length would seek callers
+	// backwards and let a manifest walk re-read the same bytes for every file it claims
+	if result < 0 {
+		return 0, errors.New("negative 7-bit encoded int")
+	}
+
 	return result, nil
 }
 

syft/pkg/cataloger/internal/dotnet/bundle/bundle_elf.go

@@ -1,11 +1,7 @@
 package bundle
 
 import (
-	"bytes"
 	"debug/elf"
-	"encoding/binary"
-	"errors"
-	"io"
 
 	"github.com/anchore/syft/syft/internal/elfutil"
 	"github.com/anchore/syft/syft/internal/unionreader"
@@ -14,51 +10,13 @@ import (
 // ExtractDepsJSONFromELFBundle extracts the deps.json content from a .net singlefile
 // bundle contained within an ELF bin
 func ExtractDepsJSONFromELFBundle(r unionreader.UnionReader) (string, error) {
-	headerOffset, err := findBundleHeaderOffsetInELF(r)
-	if err != nil || headerOffset == 0 {
-		return "", err
-	}
-	return ReadDepsJSONFromBundleHeader(r, headerOffset)
-}
-
-func findBundleHeaderOffsetInELF(r unionreader.UnionReader) (int64, error) {
 	elfFile, err := elfutil.NewFile(r)
 	if err != nil {
-		return 0, nil
+		// not an ELF, so not an ELF bundle
+		return "", nil //nolint:nilerr
 	}
 
-	elfEndOffset := calculateELFEndOffset(elfFile)
-	if elfEndOffset == 0 {
-		return 0, nil
-	}
-
-	// clamp to the actual file size so a malformed ELF (with bogus segment/section
-	// offsets+sizes) can't drive an arbitrarily large allocation below.
-	fileSize, err := r.Seek(0, io.SeekEnd)
-	if err != nil {
-		return 0, err
-	}
-	if elfEndOffset > fileSize {
-		elfEndOffset = fileSize
-	}
-
-	if _, err := r.Seek(0, io.SeekStart); err != nil {
-		return 0, err
-	}
-
-	searchData := make([]byte, elfEndOffset)
-	n, err := io.ReadFull(r, searchData)
-	if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) {
-		return 0, err
-	}
-	searchData = searchData[:n]
-
-	idx := bytes.Index(searchData, dotNetBundleSignature)
-	if idx == -1 || idx < 8 {
-		return 0, nil
-	}
-
-	return int64(binary.LittleEndian.Uint64(searchData[idx-8 : idx])), nil
+	return ExtractDepsJSON(r, calculateELFEndOffset(elfFile))
 }
 
 func calculateELFEndOffset(f *elf.File) int64 {

syft/pkg/cataloger/internal/dotnet/bundle/bundle_elf_test.go

@@ -2,6 +2,7 @@ package bundle
 
 import (
 	"bytes"
+	"debug/elf"
 	"encoding/binary"
 	"testing"
 
@@ -16,10 +17,36 @@ type readSeekCloser struct {
 
 func (readSeekCloser) Close() error { return nil }
 
-// buildELFWithHugeFilesz returns a minimal, parseable ELF64 whose single program header
-// declares an absurd p_filesz. calculateELFEndOffset will compute a huge end offset; the
-// clamp in findBundleHeaderOffsetInELF must keep the allocation bounded to the real file.
+// buildELFWithHugeFilesz returns a minimal, parseable ELF64 whose single program header declares a
+// p_filesz far past the real file. calculateELFEndOffset will compute an 8GB end offset; the bound in
+// FindSignatureOffset must keep the allocation tied to the real file.
+//
+// note: 8GB rather than something astronomical on purpose. `make([]byte, 1<<60)` panics on its own, so a
+// test built on that value passes whether or not the bound exists; `make([]byte, 8<<30)` succeeds on any
+// 64-bit host from untouched anonymous mmap, so only the requested read size distinguishes them.
 func buildELFWithHugeFilesz() []byte {
+	return buildELFWithProgHeader(0, 8<<30)
+}
+
+// readSizeRecorder records the largest single Read length requested of it, which is what tells a buffer
+// sized from the file apart from one sized from the headers.
+type readSizeRecorder struct {
+	*bytes.Reader
+	maxRead int
+}
+
+func (r *readSizeRecorder) Read(p []byte) (int, error) {
+	if len(p) > r.maxRead {
+		r.maxRead = len(p)
+	}
+	return r.Reader.Read(p)
+}
+
+func (r *readSizeRecorder) Close() error { return nil }
+
+// buildELFWithProgHeader returns a minimal, parseable ELF64 with a single PT_LOAD program header
+// carrying the given p_offset and p_filesz. debug/elf does not validate either field.
+func buildELFWithProgHeader(pOffset, pFilesz uint64) []byte {
 	const (
 		ehSize  = 64
 		phSize  = 56
@@ -46,18 +73,46 @@ func buildELFWithHugeFilesz() []byte {
 
 	ph := buf[phOff:]
 	le.PutUint32(ph[0:], 1)        // p_type = PT_LOAD
-	le.PutUint64(ph[16:], 0)     // p_offset
-	le.PutUint64(ph[32:], 1<<60) // p_filesz (bogus, attacker-controlled)
-	le.PutUint64(ph[40:], 1<<60) // p_memsz
+	le.PutUint64(ph[8:], pOffset)  // p_offset (user-controlled)
+	le.PutUint64(ph[32:], pFilesz) // p_filesz (user-controlled)
+	le.PutUint64(ph[40:], pFilesz) // p_memsz
 	return buf
 }
 
-func TestExtractDepsJSONFromELFBundle_MalformedFileszDoesNotOverAllocate(t *testing.T) {
-	data := buildELFWithHugeFilesz()
+func TestExtractDepsJSONFromELFBundle_EndOffsetOverflowDoesNotPanic(t *testing.T) {
+	// calculateELFEndOffset sums these two uint64 header fields into an int64 and adds 4096, which
+	// overflows to a negative search limit. A negative is not greater than the file size, so it slips
+	// unnoticed into the search window unless a non-positive limit reads nothing.
+	data := buildELFWithProgHeader(0x7FFFFFFFFFFFF000, 0)
+	require.Negative(t, calculateELFEndOffset(mustParseELF(t, data)),
+		"expected these header values to overflow the end offset; the guard below is what this test pins")
+
 	r := readSeekCloser{bytes.NewReader(data)}
 
-	// must not OOM/panic on the bogus p_filesz, and find no bundle signature
 	content, err := ExtractDepsJSONFromELFBundle(r)
 	require.NoError(t, err)
 	assert.Empty(t, content)
 }
+
+func mustParseELF(t *testing.T, data []byte) *elf.File {
+	t.Helper()
+	f, err := elf.NewFile(bytes.NewReader(data))
+	require.NoError(t, err)
+	return f
+}
+
+func TestExtractDepsJSONFromELFBundle_MalformedFileszDoesNotOverAllocate(t *testing.T) {
+	data := buildELFWithHugeFilesz()
+
+	// sanity: the headers really do describe an end offset far past the file, so the bound is what keeps
+	// the allocation small rather than the input being small
+	require.Greater(t, calculateELFEndOffset(mustParseELF(t, data)), int64(8*1024*1024*1024))
+
+	r := &readSizeRecorder{Reader: bytes.NewReader(data)}
+
+	content, err := ExtractDepsJSONFromELFBundle(r)
+	require.NoError(t, err)
+	assert.Empty(t, content)
+	assert.LessOrEqual(t, r.maxRead, len(data),
+		"the search must be bounded by the file, not by what the program headers claim")
+}

syft/pkg/cataloger/internal/dotnet/bundle/bundle_test.go

@@ -0,0 +1,81 @@
+package bundle
+
+import (
+	"bytes"
+	"encoding/binary"
+	"math"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// fileWithSignatureAt returns a file of the given size carrying the bundle marker (8-byte header
+// offset followed by the signature) starting at sigStart.
+func fileWithSignatureAt(size, sigStart int, headerOffset uint64) []byte {
+	data := make([]byte, size)
+	binary.LittleEndian.PutUint64(data[sigStart-8:sigStart], headerOffset)
+	copy(data[sigStart:], dotNetBundleSignature)
+	return data
+}
+
+func TestFindSignatureOffset(t *testing.T) { //nolint:funlen
+	const withMarker = 256
+
+	tests := []struct {
+		name        string
+		data        []byte
+		searchLimit int64
+		want        int64
+	}{
+		{
+			name:        "no signature present",
+			data:        make([]byte, 512),
+			searchLimit: 512,
+		},
+		{
+			name:        "zero limit searches nothing",
+			data:        fileWithSignatureAt(withMarker, 64, 0x1234),
+			searchLimit: 0,
+		},
+		{
+			// callers sum unsigned header fields into an int64, which overflows to a negative limit for
+			// some header values. This must read nothing rather than sizing a buffer from it.
+			name:        "negative limit reads nothing",
+			data:        fileWithSignatureAt(withMarker, 64, 0x1234),
+			searchLimit: math.MinInt64,
+		},
+		{
+			name:        "limit past end of file reads only what exists",
+			data:        fileWithSignatureAt(withMarker, 64, 0x1234),
+			searchLimit: math.MaxInt64 / 2,
+			want:        0x1234,
+		},
+		{
+			// the bound must not shrink the window below the real file, or a legitimate marker stops being found
+			name:        "limit inside the file still finds the marker",
+			data:        fileWithSignatureAt(withMarker, 64, 0x1234),
+			searchLimit: 128,
+			want:        0x1234,
+		},
+		{
+			name:        "limit truncates the window before the marker",
+			data:        fileWithSignatureAt(withMarker, 64, 0x1234),
+			searchLimit: 32,
+		},
+		{
+			// there is no room for the 8-byte header offset before the signature
+			name:        "signature too close to the start to carry an offset",
+			data:        append(append([]byte{0, 0}, dotNetBundleSignature...), make([]byte, 32)...),
+			searchLimit: 128,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := findSignatureOffset(bytes.NewReader(tt.data), tt.searchLimit)
+			require.NoError(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}

syft/pkg/cataloger/internal/dotnet/pe/bundle.go

@@ -1,23 +1,12 @@
 package pe
 
 import (
-	"bytes"
 	"debug/pe"
-	"encoding/binary"
-	"errors"
 	"io"
 
 	"github.com/anchore/syft/syft/pkg/cataloger/internal/dotnet/bundle"
 )
 
-// dotNetBundleSignature is the SHA-256 hash of ".net core bundle" used to identify single-file bundles.
-var dotNetBundleSignature = []byte{
-	0x8b, 0x12, 0x02, 0xb9, 0x6a, 0x61, 0x20, 0x38,
-	0x72, 0x7b, 0x93, 0x02, 0x14, 0xd7, 0xa0, 0x32,
-	0x13, 0xf5, 0xb9, 0xe6, 0xef, 0xae, 0x33, 0x18,
-	0xee, 0x3b, 0x2d, 0xce, 0x24, 0xb3, 0x6a, 0xae,
-}
-
 // ExtractDepsJSONFromBundle searches for an embedded deps.json file in a .NET single-file bundle.
 // When built with PublishSingleFile=true, .NET embeds the application and all dependencies into
 // the AppHost executable. The bundle marker (8-byte header offset + 32-byte signature) is placed
@@ -51,41 +40,7 @@ var dotNetBundleSignature = []byte{
 // - https://github.com/dotnet/runtime/blob/main/src/native/corehost/bundle/file_entry.h
 // - https://github.com/dotnet/runtime/blob/main/src/native/corehost/bundle/file_type.h
 func extractDepsJSONFromBundle(r io.ReadSeeker, sections []pe.SectionHeader32) (string, error) {
-	headerOffset, err := findBundleHeaderOffset(r, sections)
-	if err != nil {
-		return "", err
-	}
-	if headerOffset == 0 {
-		return "", nil // not a .NET single-file bundle
-	}
-
-	return bundle.ReadDepsJSONFromBundleHeader(r, headerOffset)
-}
-
-// findBundleHeaderOffset locates the bundle marker within the PE structure and returns the header offset.
-// Returns 0 if no bundle marker is found (not a single-file bundle).
-func findBundleHeaderOffset(r io.ReadSeeker, sections []pe.SectionHeader32) (int64, error) {
-	peEndOffset := calculatePEEndOffset(sections)
-
-	if _, err := r.Seek(0, io.SeekStart); err != nil {
-		return 0, err
-	}
-
-	peData := make([]byte, peEndOffset)
-	n, err := io.ReadFull(r, peData)
-	if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) {
-		return 0, err
-	}
-	peData = peData[:n]
-
-	idx := bytes.Index(peData, dotNetBundleSignature)
-	if idx == -1 || idx < 8 {
-		return 0, nil
-	}
-
-	// the header offset is stored in the 8 bytes immediately before the signature
-	headerOffset := int64(binary.LittleEndian.Uint64(peData[idx-8 : idx]))
-	return headerOffset, nil
+	return bundle.ExtractDepsJSON(r, calculatePEEndOffset(sections))
 }
 
 // calculatePEEndOffset determines where the PE structure ends based on section headers,

syft/pkg/cataloger/internal/dotnet/pe/bundle_test.go

@@ -1,6 +1,8 @@
 package pe
 
 import (
+	"bytes"
+	"debug/pe"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -56,3 +58,37 @@ func Test_extractDepsJSONFromBundle_Versions(t *testing.T) {
 		})
 	}
 }
+
+// readSizeRecorder records the largest single Read length requested of it. The worst end offset PE
+// headers can describe is about 8.6GB, and `make([]byte, 8.6e9)` succeeds on any 64-bit host from fresh
+// anonymous mmap without touching the pages, so asserting "no panic" would pass with or without the
+// bound. The requested read size is what actually distinguishes them.
+type readSizeRecorder struct {
+	*bytes.Reader
+	maxRead int
+}
+
+func (r *readSizeRecorder) Read(p []byte) (int, error) {
+	if len(p) > r.maxRead {
+		r.maxRead = len(p)
+	}
+	return r.Reader.Read(p)
+}
+
+func TestExtractDepsJSONFromBundle_MalformedSectionSizesDoNotOverAllocate(t *testing.T) {
+	// PointerToRawData and SizeOfRawData are user-controlled and unrelated to the real file size
+	sections := []pe.SectionHeader32{{PointerToRawData: 0xFFFFFFFF, SizeOfRawData: 0xFFFFFFFF}}
+
+	// sanity: the headers really do describe an end offset far past the file, so the bound is what keeps
+	// the allocation small rather than the input being small
+	require.Greater(t, calculatePEEndOffset(sections), int64(8*1024*1024*1024))
+
+	const fileSize = 512 // a small "file" with no bundle signature
+	r := &readSizeRecorder{Reader: bytes.NewReader(make([]byte, fileSize))}
+
+	content, err := extractDepsJSONFromBundle(r, sections)
+	require.NoError(t, err)
+	assert.Empty(t, content)
+	assert.LessOrEqual(t, r.maxRead, fileSize,
+		"the search must be bounded by the file, not by what the section headers claim")
+}