encoding/pem: Decode method uses extensive CPU when providing large data #50116
Description
What version of Go are you using (go version)?
$ go version 17.5
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 go env GO111MODULE="" GOARCH="amd64" GOBIN="/home/sammy/go/bin" GOCACHE="/home/sammy/.cache/go-build" GOENV="/home/sammy/.config/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="linux" GOINSECURE="" GOMODCACHE="/home/sammy/go/pkg/mod" GONOPROXY="" GONOSUMDB="" GOOS="linux" GOPATH="/home/sammy/go" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/nix/store/i8x0bv8v69j8c2njymgs4cl3albqc20h-go-1.17.5/share/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/nix/store/i8x0bv8v69j8c2njymgs4cl3albqc20h-go-1.17.5/share/go/pkg/tool/linux_amd64" GOVCS="" GOVERSION="go1.17.5" GCCGO="gccgo" AR="ar" CC="gcc" CXX="g++" CGO_ENABLED="1" GOMOD="/dev/null" CGO_CFLAGS="-g -O2" CGO_CPPFLAGS="" CGO_CXXFLAGS="-g -O2" CGO_FFLAGS="-g -O2" CGO_LDFLAGS="-g -O2" PKG_CONFIG="pkg-config" GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/run/user/1000/go-build3984378223=/tmp/go-build -gno-record-gcc-switches"
What did you do?
As part of fuzz testing sigstore/sigstore#188 using oss-fuzz we ran into an issue where the pem.Decode is consuming extensive CPU and here is the test case for it https://github.com/sigstore/sigstore/files/7676542/clusterfuzz-testcase-minimized-FuzzUnmarshalCertificatesFromPEM-4710187355734016.zip
What did you expect to see?
The pem.Decode finishing sooner than it consumes large amount of CPU
What did you see instead?
It being slow