debug/elf: Incorrectly double-decompressing ELF section #59208
Description
What version of Go are you using (go version)?
$ go version go version go1.20.1 darwin/arm64
Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (go env)?
go env Output
$ go env GO111MODULE="" GOARCH="arm64" GOBIN="/Users/brancz/bin" GOCACHE="/Users/brancz/Library/Caches/go-build" GOENV="/Users/brancz/Library/Application Support/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="arm64" GOHOSTOS="darwin" GOINSECURE="" GOMODCACHE="/Users/brancz/pkg/mod" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/brancz" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/opt/homebrew/Cellar/go/1.20.1/libexec" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/opt/homebrew/Cellar/go/1.20.1/libexec/pkg/tool/darwin_arm64" GOVCS="" GOVERSION="go1.20.1" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/Users/brancz/src/github.com/polarsignals/polarsignals/go.mod" GOWORK="" CGO_CFLAGS="-O2 -g" CGO_CPPFLAGS="" CGO_CXXFLAGS="-O2 -g" CGO_FFLAGS="-O2 -g" CGO_LDFLAGS="-O2 -g" PKG_CONFIG="pkg-config" GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/var/folders/rl/8sh8jb5s1c1fl77ztzy4zw6m0000gn/T/go-build2747742421=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
Downloaded the debuginfo for liblzma5:
curl https://debuginfod.ubuntu.com/buildid/0e13b0f27b3bc79a2828c11199ce4336a348af37/debuginfo > liblzma5.debuginfo
Tried to look at the DWARF entries:
package main
import (
"bytes"
"debug/elf"
"fmt"
"io"
"net/http"
)
func main() {
resp, err := http.Get("https://debuginfod.ubuntu.com/buildid/0e13b0f27b3bc79a2828c11199ce4336a348af37/debuginfo")
if err != nil {
panic(err)
}
if resp.StatusCode != 200 {
panic("unexpected status code")
}
content, err := io.ReadAll(resp.Body)
if err != nil {
panic(err)
}
f, err := elf.NewFile(bytes.NewReader(content))
if err != nil {
panic(err)
}
_, err = f.DWARF()
fmt.Println("DWARF ERROR:", err)
}And running that returns an error:
$ go run main.go
DWARF ERROR: zlib: invalid header
What did you expect to see?
No error.
What did you see instead?
An error, and I suspect I know why: debug/elf in extremely rare cases attempts to double-decompress an ELF section.
First the call to .Data() returns the decompressed section:
Line 1308 in 0aa14fc
And if by pure chance the first 4 bytes of the decompressed bytes also happen to be what trigger a decompression, then the .DWARF() function will attempt to decompress the section a second time:
Lines 1317 to 1319 in 0aa14fc
cc @mengzhuo since you recently added this case