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Fix dns resolver for docker #435

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Fix dns resolver for docker #435

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2bc2b32
fix dns resolver for docker
sailikhith-stepsecurity Aug 28, 2024
3850ce0
fix go tests
sailikhith-stepsecurity Aug 28, 2024
909c4e3
add functionality to switch to audit mode when domain resolution fails
sailikhith-stepsecurity Aug 28, 2024
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20 changes: 16 additions & 4 deletions agent.go
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Original file line number Diff line number Diff line change
Expand Up @@ -125,10 +125,22 @@ func Run(ctx context.Context, configFilePath string, hostDNSServer DNSServer,
// this will cause domain, IP mapping to be cached
ipAddress, err := dnsProxy.getIPByDomain(domainName)
if err != nil {
WriteLog(fmt.Sprintf("Error resolving allowed domain %v", err))
WriteAnnotation(fmt.Sprintf("%s Reverting agent since allowed endpoint %s could not be resolved", StepSecurityAnnotationPrefix, strings.Trim(domainName, ".")))
RevertChanges(iptables, nflog, cmd, resolvdConfigPath, dockerDaemonConfigPath, dnsConfig, sudo)
return err
WriteLog(fmt.Sprintf("Error resolving allowed domain in Block mode %v", err))
WriteLog("Switching to Audit mode.")

// Change the policy to Audit
config.EgressPolicy = EgressPolicyAudit
apiclient.EgressPolicy = EgressPolicyAudit

// Reinitialize the Cache with the new Audit policy
Cache = InitCache(config.EgressPolicy)

// Update DNSProxy with the new cache and EgressPolicy
dnsProxy.Cache = &Cache
dnsProxy.EgressPolicy = EgressPolicyAudit

// Exit the loop as we have switched to Audit policy
break
}
for _, endpoint := range endpoints {
// create list of ip address to be added to firewall
Expand Down
4 changes: 2 additions & 2 deletions dnsconfig.go
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Expand Up @@ -25,7 +25,7 @@ const (
// https://unix.stackexchange.com/questions/508397/what-is-the-recommended-way-to-set-a-global-dns-server-override-on-a-system-usin
// Domains=~. instructs systemd-resolved to always use the global nameservers
// and to never query any DHCP-supplied nameservers
localDnsServer = "[Resolve]\nDNS=127.0.0.1\nDomains=~.\n"
localDnsServer = "[Resolve]\nDNS=127.0.0.1 172.17.0.1\nDomains=~.\n"
)

func updateDockerConfig(configPath string) error {
Expand All @@ -46,7 +46,7 @@ func updateDockerConfig(configPath string) error {
return errors.Wrap(err, "failed to unmarshal config file")
}

m["dns"] = []string{dockerDnsServer}
// m["dns"] = []string{dockerDnsServer}
m["live-restore"] = true
// m["userns-remap"] = "runner:runner" // Checkout: https://docs.docker.com/engine/security/userns-remap/#enable-userns-remap-on-the-daemon

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6 changes: 3 additions & 3 deletions dnsconfig_test.go
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Expand Up @@ -41,11 +41,11 @@ func Test_updateDockerConfig(t *testing.T) {
}{
{name: "existing file",
args: args{configPath: tmpFileName},
want: "{\"cgroup-parent\":\"/actions_job\",\"dns\":[\"172.17.0.1\"],\"live-restore\":true}",
want: "{\"cgroup-parent\":\"/actions_job\",\"live-restore\":true}",
wantErr: false},
{name: "non existent file",
args: args{configPath: mockDockerConfigPath},
want: "{\"dns\":[\"172.17.0.1\"],\"live-restore\":true}",
want: "{\"live-restore\":true}",
wantErr: false},
}

Expand Down Expand Up @@ -79,7 +79,7 @@ func Test_writeResolveConfig(t *testing.T) {
}{
{name: "overwrite file",
args: args{configPath: tmpFileName},
want: "[Resolve]\nDNS=127.0.0.1\nDomains=~.\n",
want: "[Resolve]\nDNS=127.0.0.1 172.17.0.1\nDomains=~.\n",
wantErr: false},
}
for _, tt := range tests {
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