debug/elf: return error in DynValue for invalid dynamic section size

This is a follow-up to CL 536400.

Fixes #64446

Author: callthingsoff

src/debug/elf/file.go

@@ -1659,6 +1659,14 @@ func (f *File) DynValue(tag DynTag) ([]uint64, error) {
 	// Parse the .dynamic section as a string of bytes.
 	var vals []uint64
 	for len(d) > 0 {
+		dynSize := 8
+		if f.Class == ELFCLASS64 {
+			dynSize = 16
+		}
+		if len(d)%dynSize != 0 {
+			return nil, errors.New("length of dynamic section is not a multiple of dynamic entry size")
+		}
+
 		var t DynTag
 		var v uint64
 		switch f.Class {