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Add warning for --dns flag set to localhost addresses.

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We should warn users who use the `--dns` command line option to point
DNS to a localhost address, either IPv4 or IPv6.  Unless they have
specifically set up the container as a DNS server or are using
--net=host (which is why this should be allowed, but warned on because
those are pretty unique cases) a localhost address as a resolver will
not reach what they might expect (e.g. expecting it will hit localhost
on the Docker daemon/host).

Added a test for the message, and fixed up tests to separate stdout and
stderr that were using `--dns=127.0.0.1` to test the options.

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
This commit is contained in:
Phil Estes 2015-03-10 10:22:29 -04:00
parent 02e0a23d80
commit afa92a9af0
3 changed files with 35 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
api/client/commands.go
View file

@ -37,6 +37,7 @@ import (
"github.com/docker/docker/pkg/fileutils"
"github.com/docker/docker/pkg/homedir"
flag "github.com/docker/docker/pkg/mflag"
"github.com/docker/docker/pkg/networkfs/resolvconf"
"github.com/docker/docker/pkg/parsers"
"github.com/docker/docker/pkg/parsers/filters"
"github.com/docker/docker/pkg/promise"
@ -2263,6 +2264,18 @@ func (cli *DockerCli) CmdRun(args ...string) error {
if err != nil {
utils.ReportError(cmd, err.Error(), true)
}
if len(hostConfig.Dns) > 0 {
// check the DNS settings passed via --dns against
// localhost regexp to warn if they are trying to
// set a DNS to a localhost address
for _, dnsIP := range hostConfig.Dns {
if resolvconf.IsLocalhost(dnsIP) {
fmt.Fprintf(cli.err, "WARNING: Localhost DNS setting (--dns=%s) may fail in containers.\n", dnsIP)
break
}
}
}
if config.Image == "" {
cmd.Usage()
return nil

11
integration-cli/docker_cli_run_test.go
View file

@ -1463,11 +1463,16 @@ func TestRunDnsOptions(t *testing.T) {
cmd := exec.Command(dockerBinary, "run", "--dns=127.0.0.1", "--dns-search=mydomain", "busybox", "cat", "/etc/resolv.conf")
out, _, err := runCommandWithOutput(cmd)
out, stderr, _, err := runCommandWithStdoutStderr(cmd)
if err != nil {
t.Fatal(err, out)
}
// The client will get a warning on stderr when setting DNS to a localhost address; verify this:
if !strings.Contains(stderr, "Localhost DNS setting") {
t.Fatalf("Expected warning on stderr about localhost resolver, but got %q", stderr)
}
actual := strings.Replace(strings.Trim(out, "\r\n"), "\n", " ", -1)
if actual != "nameserver 127.0.0.1 search mydomain" {
t.Fatalf("expected 'nameserver 127.0.0.1 search mydomain', but says: %q", actual)
@ -1475,7 +1480,7 @@ func TestRunDnsOptions(t *testing.T) {
cmd = exec.Command(dockerBinary, "run", "--dns=127.0.0.1", "--dns-search=.", "busybox", "cat", "/etc/resolv.conf")
out, _, err = runCommandWithOutput(cmd)
out, _, _, err = runCommandWithStdoutStderr(cmd)
if err != nil {
t.Fatal(err, out)
}
@ -1502,7 +1507,7 @@ func TestRunDnsOptionsBasedOnHostResolvConf(t *testing.T) {
var out string
cmd := exec.Command(dockerBinary, "run", "--dns=127.0.0.1", "busybox", "cat", "/etc/resolv.conf")
if out, _, err = runCommandWithOutput(cmd); err != nil {
if out, _, _, err = runCommandWithStdoutStderr(cmd); err != nil {
t.Fatal(err, out)
}

19
pkg/networkfs/resolvconf/resolvconf.go
View file

@ -23,11 +23,13 @@ var (
// For readability and sufficiency for Docker purposes this seemed more reasonable than a
// 1000+ character regexp with exact and complete IPv6 validation
ipv6Address = `([0-9A-Fa-f]{0,4}:){2,7}([0-9A-Fa-f]{0,4})`
ipLocalhost = `((127\.([0-9]{1,3}.){2}[0-9]{1,3})|(::1))`
localhostRegexp = regexp.MustCompile(`(?m)^nameserver\s+((127\.([0-9]{1,3}.){2}[0-9]{1,3})|(::1))\s*\n*`)
nsIPv6Regexp = regexp.MustCompile(`(?m)^nameserver\s+` + ipv6Address + `\s*\n*`)
nsRegexp = regexp.MustCompile(`^\s*nameserver\s*((` + ipv4Address + `)|(` + ipv6Address + `))\s*$`)
searchRegexp = regexp.MustCompile(`^\s*search\s*(([^\s]+\s*)*)$`)
localhostIPRegexp = regexp.MustCompile(ipLocalhost)
localhostNSRegexp = regexp.MustCompile(`(?m)^nameserver\s+` + ipLocalhost + `\s*\n*`)
nsIPv6Regexp = regexp.MustCompile(`(?m)^nameserver\s+` + ipv6Address + `\s*\n*`)
nsRegexp = regexp.MustCompile(`^\s*nameserver\s*((` + ipv4Address + `)|(` + ipv6Address + `))\s*$`)
searchRegexp = regexp.MustCompile(`^\s*search\s*(([^\s]+\s*)*)$`)
)
var lastModified struct {
@ -87,7 +89,7 @@ func GetLastModified() ([]byte, string) {
// It also returns a boolean to notify the caller if changes were made at all
func FilterResolvDns(resolvConf []byte, ipv6Enabled bool) ([]byte, bool) {
changed := false
cleanedResolvConf := localhostRegexp.ReplaceAll(resolvConf, []byte{})
cleanedResolvConf := localhostNSRegexp.ReplaceAll(resolvConf, []byte{})
// if IPv6 is not enabled, also clean out any IPv6 address nameserver
if !ipv6Enabled {
cleanedResolvConf = nsIPv6Regexp.ReplaceAll(cleanedResolvConf, []byte{})
@ -124,6 +126,13 @@ func getLines(input []byte, commentMarker []byte) [][]byte {
return output
}
// returns true if the IP string matches the localhost IP regular expression.
// Used for determining if nameserver settings are being passed which are
// localhost addresses
func IsLocalhost(ip string) bool {
return localhostIPRegexp.MatchString(ip)
}
// GetNameservers returns nameservers (if any) listed in /etc/resolv.conf
func GetNameservers(resolvConf []byte) []string {
nameservers := []string{}