net/dns: ensure /etc/resolv.conf is world-readable even with a umask

Previously, if we had a umask set (e.g. 0027) that prevented creating a
world-readable file, /etc/resolv.conf would be created without the o+r
bit and thus other users may be unable to resolve DNS.

Since a umask only applies to file creation, chmod the file after
creation and before renaming it to ensure that it has the appropriate
permissions.

Updates #12609

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I2a05d64f4f3a8ee8683a70be17a7da0e70933137

net/dns/wsl_windows.go

@@ -159,6 +159,10 @@ func (fs wslFS) Stat(name string) (isRegular bool, err error) {
 	return true, nil
 }
 
+func (fs wslFS) Chmod(name string, perm os.FileMode) error {
+	return wslRun(fs.cmd("chmod", "--", fmt.Sprintf("%04o", perm), name))
+}
+
 func (fs wslFS) Rename(oldName, newName string) error {
 	return wslRun(fs.cmd("mv", "--", oldName, newName))
 }