debug/pe: slice bounds out of range panic

[monoidic]

Go version

go version go1.24.2 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build890824037=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/home/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/snap/go/10888'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/home/user/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/snap/go/10888/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.2'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I attempted to automatically analyze the executables on a Windows host. As a part of that, debug/pe.File.ImportedSymbols() was called.
This failed on the official Windows Word .exe file with a "slice bounds out of range" error.
https://go.dev/play/p/K1_mQcc4Fbd
Minimal example which produces the same error with just the first 32k bytes of winword.exe.
If required, I can share the full file itself as well. Though I am not 100% sure about the licensing terms of sharing winword.exe

What did you see happen?

Slice bounds out of error panic, as is visible in the Go Playground link.

panic: runtime error: slice bounds out of range [4294947512:512]

goroutine 1 [running]:
debug/pe.(*File).ImportedSymbols(0x50a608?)
	/usr/local/go-faketime/src/debug/pe/file.go:411 +0x949
main.main()
	/tmp/sandbox1960551843/prog.go:16 +0x186

What did you expect to see?

A slice with the names of the symbols, as the documentation states.

[gabyhelp]

Related Issues

• debug/elf: slice bounds out of range in Symbols #62649 (closed)
• debug/pe: attempt to allocate giant slice #17809 (closed)
• debug/pe: slice bounds out of range #30253 (closed)
• debug/pe: Calling File.ImportedLibraries returns an empty slice #48039
• debug/elf: slice bounds out of range #10999 (closed)
• debug/elf: slice out of bounds in ImportedLibraries #63610 (closed)
• debug/pe: TestInternalLinkerDWARF fail in windows #64200 (closed)
• x/tools/cmd/gopls: crashes with "slice bounds out of range" #31707 (closed)
• cmd/go: slice bounds out of range in test #14337 (closed)
• cmd/link: slice bounds out of range #62098 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[randall77]

@alexbrainman @golang/windows

[monoidic]

It does seem that a good number of PE parsers stumble a bit on this file, actually.
The Rust pelite library gives a "unaligned" error unless unsafe_alignment is used, disabling alignment checks.
pestudio displays garbled text.
PE-Bear and the Python pefile library seem to work just fine.

[gopherbot]

Change https://go.dev/cl/684495 mentions this issue: debug/pe: avoid panic in File.ImportedSymbols

[alexbrainman]

@monoidic please check if https://go.dev/cl/684495 fixes your problem.

Thank you.

Alex

[monoidic]

Indeed, it no longer panics.
I suspect there may be some way this value is meant to be parsed (enum or some special parsing rules etc), which was parsed by PE-Bear as seen below, though I could not immediately figure out what it was. At least there's no panic now.
Attached are PE-Bear's results.

[odeke-em]

Nice work and thank you @alexbrainman for the fix, thank you @monoidic for the detailed issue and Keith for the tag. Alex, kindly please rebase from master and I have also kindly tagged @ianlancetaylor to the CL for review. Thank you.

[odeke-em]

@alexbrainman I have a vector that still crashes despite your CL fix per https://go.dev/play/p/jo0icuZyv1M or

data := []byte("MZ0000000000000000000000000000000000000000000000000000000000\x10\x01\x00\x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000PE\x00\x00d\x86\b\x000000\x00\x00\x00\x000000\xf0\x0000\v\x020000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\x10\x00\x00\x00000000000\xb0\x00\x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000\x00\x0000000000000000000000\x00\x000000000000000000\x00\x0000000000000000000000\x00\x000000000000000000\x00\x00\x000000000000000000000\x00\x00000000000000000 \x00\x00\x000000000000000000000\x00\x00000000000000000\x00\x00\x0000000000000000000000\x00\x000000000000000000000\xb0\x00\x000\x02\x00\x000\x00\x00\x0000000000\x00\x0000000000000000000000000000000000000000\x00\x0000000000000000000000000000000000000000\x00\x00000000")

and the correct fix would be to perform the following

diff --git a/src/debug/pe/file.go b/src/debug/pe/file.go
index ed63a11cb6..ea28d51628 100644
--- a/src/debug/pe/file.go
+++ b/src/debug/pe/file.go
@@ -408,6 +412,9 @@ func (f *File) ImportedSymbols() ([]string, error) {
 		dt.dll, _ = getString(names, int(dt.Name-ds.VirtualAddress))
 		d, _ = ds.Data()
 		// seek to OriginalFirstThunk
+		if diff := dt.OriginalFirstThunk - ds.VirtualAddress; diff >= uint32(len(d)) {
+			continue
+		}
 		d = d[dt.OriginalFirstThunk-ds.VirtualAddress:]
 		for len(d) > 0 {
 			if pe64 { // 64bit