Revert "crypto/rand: add randcrash=0 GODEBUG"

A GODEBUG is actually a security risk here: most programs will start to
ignore errors from Read because they can't happen (which is the intended
behavior), but then if a program is run with GODEBUG=randcrash=0 it will
use a partial buffer in case an error occurs, which may be catastrophic.

Note that the proposal was accepted without the GODEBUG, which was only
added later.

This (partially) reverts CL 608435. I kept the tests.

Updates #66821

Change-Id: I3fd20f9cae0d34115133fe935f0cfc7a741a2662
Reviewed-on: https://go-review.googlesource.com/c/go/+/622115
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>
Auto-Submit: Filippo Valsorda <[email protected]>
Reviewed-by: Daniel McCarney <[email protected]>

Author: FiloSottile

Diff for: doc/godebug.md

@@ -168,11 +168,6 @@ For Go 1.24, it now defaults to multipathtcp="2", thus
 enabled by default on listerners. Using multipathtcp="0" reverts to the
 pre-Go 1.24 behavior.
 
-Go 1.24 changed [`crypto/rand.Read`](/pkg/crypto/rand/#Read) to crash the
-program on any error. This setting is controlled by the `randcrash` setting.
-For Go 1.24 it defaults to `randcrash=1`.
-Using `randcrash=0` reverts to the pre-Go 1.24 behavior.
-
 ### Go 1.23
 
 Go 1.23 changed the channels created by package time to be unbuffered

Diff for: src/crypto/rand/rand.go

@@ -8,7 +8,6 @@ package rand
 
 import (
 	"crypto/internal/boring"
-	"internal/godebug"
 	"io"
 	"os"
 	"sync"
@@ -65,8 +64,6 @@ func (r *reader) Read(b []byte) (n int, err error) {
 //go:linkname fatal
 func fatal(string)
 
-var randcrash = godebug.New("randcrash")
-
 // Read fills b with cryptographically secure random bytes. It never returns an
 // error, and always fills b entirely.
 //
@@ -86,10 +83,6 @@ func Read(b []byte) (n int, err error) {
 		copy(b, bb)
 	}
 	if err != nil {
-		if randcrash.Value() == "0" {
-			randcrash.IncNonDefault()
-			return 0, err
-		}
 		fatal("crypto/rand: failed to read random data (see https://go.dev/issue/66821): " + err.Error())
 		panic("unreachable") // To be sure.
 	}

Diff for: src/crypto/rand/rand_test.go

@@ -198,8 +198,7 @@ func TestReadError(t *testing.T) {
 	}
 	testenv.MustHaveExec(t)
 
-	// We run this test in a subprocess because it's expected to crash the
-	// program unless the GODEBUG is set.
+	// We run this test in a subprocess because it's expected to crash.
 	if os.Getenv("GO_TEST_READ_ERROR") == "1" {
 		defer func(r io.Reader) { Reader = r }(Reader)
 		Reader = readerFunc(func([]byte) (int, error) {
@@ -221,13 +220,6 @@ func TestReadError(t *testing.T) {
 	if !bytes.Contains(out, []byte(exp)) {
 		t.Errorf("subprocess output does not contain %q: %s", exp, out)
 	}
-
-	cmd = testenv.Command(t, os.Args[0], "-test.run=TestReadError")
-	cmd.Env = append(os.Environ(), "GO_TEST_READ_ERROR=1", "GODEBUG=randcrash=0")
-	out, err = cmd.CombinedOutput()
-	if err != nil {
-		t.Errorf("subprocess failed: %v\n%s", err, out)
-	}
 }
 
 func BenchmarkRead(b *testing.B) {

Diff for: src/internal/godebugs/table.go

@@ -47,7 +47,6 @@ var All = []Info{
 	{Name: "netedns0", Package: "net", Changed: 19, Old: "0"},
 	{Name: "panicnil", Package: "runtime", Changed: 21, Old: "1"},
 	{Name: "randautoseed", Package: "math/rand"},
-	{Name: "randcrash", Package: "crypto/rand", Changed: 24, Old: "0"},
 	{Name: "randseednop", Package: "math/rand", Changed: 24, Old: "0"},
 	{Name: "tarinsecurepath", Package: "archive/tar"},
 	{Name: "tls10server", Package: "crypto/tls", Changed: 22, Old: "1"},

Diff for: src/runtime/metrics/doc.go

@@ -306,10 +306,6 @@ Below is the full list of supported metrics, ordered lexicographically.
 		The number of non-default behaviors executed by the math/rand
 		package due to a non-default GODEBUG=randautoseed=... setting.
 
-	/godebug/non-default-behavior/randcrash:events
-		The number of non-default behaviors executed by the crypto/rand
-		package due to a non-default GODEBUG=randcrash=... setting.
-
 	/godebug/non-default-behavior/randseednop:events
 		The number of non-default behaviors executed by the math/rand
 		package due to a non-default GODEBUG=randseednop=... setting.