Modify /etc/resolv.conf when connecting/disconnecting

The `podman network connect` and `podman network disconnect`
commands give containers access to different networks than the
ones they were created with; these networks can also have DNS
servers associated with them. Until now, however, we did not
modify resolv.conf as network membership changed.

With this PR, `podman network connect` will add any new
nameservers supported by the new network to the container's
/etc/resolv.conf, and `podman network disconnect` command will do
the opposite, removing the network's nameservers from
`/etc/resolv.conf`.

Fixes #9603

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

1 files changed, 31 insertions, 0 deletions

diff --git a/test/e2e/network_connect_disconnect_test.go b/test/e2e/network_connect_disconnect_test.go
index baef142ba..a0716c84d 100644
--- a/test/e2e/network_connect_disconnect_test.go
+++ b/test/e2e/network_connect_disconnect_test.go
@@ -2,6 +2,7 @@ package integration
 
 import (
 	"os"
+	"strings"
 
 	. "github.com/containers/podman/v4/test/utils"
 	"github.com/containers/storage/pkg/stringid"
@@ -77,6 +78,11 @@ var _ = Describe("Podman network connect and disconnect", func() {
 		Expect(session).Should(Exit(0))
 		defer podmanTest.removeNetwork(netName)
 
+		gw := podmanTest.Podman([]string{"network", "inspect", netName, "--format", "{{(index .Subnets 0).Gateway}}"})
+		gw.WaitWithDefaultTimeout()
+		Expect(gw).Should(Exit(0))
+		ns := gw.OutputToString()
+
 		ctr := podmanTest.Podman([]string{"run", "-dt", "--name", "test", "--network", netName, ALPINE, "top"})
 		ctr.WaitWithDefaultTimeout()
 		Expect(ctr).Should(Exit(0))
@@ -85,6 +91,11 @@ var _ = Describe("Podman network connect and disconnect", func() {
 		exec.WaitWithDefaultTimeout()
 		Expect(exec).Should(Exit(0))
 
+		exec2 := podmanTest.Podman([]string{"exec", "-it", "test", "cat", "/etc/resolv.conf"})
+		exec2.WaitWithDefaultTimeout()
+		Expect(exec2).Should(Exit(0))
+		Expect(strings.Contains(exec2.OutputToString(), ns)).To(BeTrue())
+
 		dis := podmanTest.Podman([]string{"network", "disconnect", netName, "test"})
 		dis.WaitWithDefaultTimeout()
 		Expect(dis).Should(Exit(0))
@@ -98,6 +109,11 @@ var _ = Describe("Podman network connect and disconnect", func() {
 		exec = podmanTest.Podman([]string{"exec", "-it", "test", "ip", "addr", "show", "eth0"})
 		exec.WaitWithDefaultTimeout()
 		Expect(exec).Should(ExitWithError())
+
+		exec3 := podmanTest.Podman([]string{"exec", "-it", "test", "cat", "/etc/resolv.conf"})
+		exec3.WaitWithDefaultTimeout()
+		Expect(exec3).Should(Exit(0))
+		Expect(strings.Contains(exec3.OutputToString(), ns)).To(BeFalse())
 	})
 
 	It("bad network name in connect should result in error", func() {
@@ -182,6 +198,16 @@ var _ = Describe("Podman network connect and disconnect", func() {
 		Expect(session).Should(Exit(0))
 		defer podmanTest.removeNetwork(newNetName)
 
+		gw := podmanTest.Podman([]string{"network", "inspect", newNetName, "--format", "{{(index .Subnets 0).Gateway}}"})
+		gw.WaitWithDefaultTimeout()
+		Expect(gw).Should(Exit(0))
+		ns := gw.OutputToString()
+
+		exec2 := podmanTest.Podman([]string{"exec", "-it", "test", "cat", "/etc/resolv.conf"})
+		exec2.WaitWithDefaultTimeout()
+		Expect(exec2).Should(Exit(0))
+		Expect(strings.Contains(exec2.OutputToString(), ns)).To(BeFalse())
+
 		ip := "10.11.100.99"
 		mac := "44:11:44:11:44:11"
 		connect := podmanTest.Podman([]string{"network", "connect", "--ip", ip, "--mac-address", mac, newNetName, "test"})
@@ -206,6 +232,11 @@ var _ = Describe("Podman network connect and disconnect", func() {
 		Expect(exec.OutputToString()).Should(ContainSubstring(ip))
 		Expect(exec.OutputToString()).Should(ContainSubstring(mac))
 
+		exec3 := podmanTest.Podman([]string{"exec", "-it", "test", "cat", "/etc/resolv.conf"})
+		exec3.WaitWithDefaultTimeout()
+		Expect(exec3).Should(Exit(0))
+		Expect(strings.Contains(exec3.OutputToString(), ns)).To(BeTrue())
+
 		// make sure no logrus errors are shown https://github.com/containers/podman/issues/9602
 		rm := podmanTest.Podman([]string{"rm", "--time=0", "-f", "test"})
 		rm.WaitWithDefaultTimeout()