x/tools/internal/fastwalk: problem with processing long file names

[mikolajb]

What version of Go are you using (go version)?

$ go version
go version go1.11.2 linux/amd64

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
GOARCH="amd64"
GOBIN="/home/mikolaj/go/bin"
GOCACHE="/home/mikolaj/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/mikolaj/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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=/tmp/go-build664414908=/tmp/go-build -gno-record-gcc-switches"

What did you do?

fastwalk.direntNamlen() crashes while producing a long filename (e.g., 255 characters).

What did you expect to see?

not to crash

What did you see instead?

panic: runtime error: slice bounds out of range [recovered]
	panic: runtime error: slice bounds out of range

goroutine 5 [running]:
testing.tRunner.func1(0xc0000ae100)
	/usr/lib/go/src/testing/testing.go:792 +0x387
panic(0x51db00, 0x62dff0)
	/usr/lib/go/src/runtime/panic.go:513 +0x1b9
golang.org/x/tools/internal/fastwalk.direntNamlen(0xc0000bff00, 0x0)
	/home/mikolaj/go/src/golang.org/x/tools/internal/fastwalk/fastwalk_dirent_namlen_linux.go:19 +0x96
golang.org/x/tools/internal/fastwalk.parseDirEnt(0xc0000bff00, 0x118, 0x1fb0, 0x7, 0xc000000000, 0x0, 0x0)
	/home/mikolaj/go/src/golang.org/x/tools/internal/fastwalk/fastwalk_unix.go:116 +0x94
golang.org/x/tools/internal/fastwalk.readDir(0x5439c6, 0x6, 0xc0000c1f20, 0x0, 0x0)
	/home/mikolaj/go/src/golang.org/x/tools/internal/fastwalk/fastwalk_unix.go:46 +0x14c
golang.org/x/tools/internal/fastwalk.(*walker).walk(0xc000070300, 0x5439c6, 0x6, 0x9406d00, 0x9406d81005f6818, 0x5be70f07)
	/home/mikolaj/go/src/golang.org/x/tools/internal/fastwalk/fastwalk.go:195 +0x6a
golang.org/x/tools/internal/fastwalk.TestOnSomething(0xc0000ae100)
	/home/mikolaj/go/src/golang.org/x/tools/internal/fastwalk/fastwalk_dirent_namlen_linux_test.go:21 +0x14b
testing.tRunner(0xc0000ae100, 0x54c948)
	/usr/lib/go/src/testing/testing.go:827 +0xbf
created by testing.(*T).Run
	/usr/lib/go/src/testing/testing.go:878 +0x353

[ianlancetaylor]

See https://golang.org/cl/148884

[gopherbot]

Change https://golang.org/cl/148884 mentions this issue: internal/fastwalk: avoids slice bounds out of range for long file names