Make changes to /etc/passwd on disk for non-read only

Bind-mounting /etc/passwd into the container is problematic
becuase of how system utilities like `useradd` work. They want
to make a copy and then rename to try to prevent breakage; this
is, unfortunately, impossible when the file they want to rename
is a bind mount. The current behavior is fine for read-only
containers, though, because we expect useradd to fail in those
cases.

Instead of bind-mounting, we can edit /etc/passwd in the
container's rootfs. This is kind of gross, because the change
will show up in `podman diff` and similar tools, and will be
included in images made by `podman commit`. However, it's a lot
better than breaking important system tools.

Fixes #6953

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

1 files changed, 25 insertions, 0 deletions

diff --git a/test/e2e/run_userns_test.go b/test/e2e/run_userns_test.go
index 42f13537d..2ddb84a94 100644
--- a/test/e2e/run_userns_test.go
+++ b/test/e2e/run_userns_test.go
@@ -113,6 +113,31 @@ var _ = Describe("Podman UserNS support", func() {
 		Expect(session.OutputToString()).To(Equal("0"))
 	})
 
+	It("podman run --userns=keep-id can add users", func() {
+		if os.Geteuid() == 0 {
+			Skip("Test only runs without root")
+		}
+
+		userName := os.Getenv("USER")
+		if userName == "" {
+			Skip("Can't complete test if no username available")
+		}
+
+		ctrName := "ctr-name"
+		session := podmanTest.Podman([]string{"run", "--userns=keep-id", "--user", "root:root", "-d", "--stop-signal", "9", "--name", ctrName, fedoraMinimal, "sleep", "600"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+
+		exec1 := podmanTest.Podman([]string{"exec", "-t", "-i", ctrName, "cat", "/etc/passwd"})
+		exec1.WaitWithDefaultTimeout()
+		Expect(exec1.ExitCode()).To(Equal(0))
+		Expect(exec1.OutputToString()).To(ContainSubstring(userName))
+
+		exec2 := podmanTest.Podman([]string{"exec", "-t", "-i", ctrName, "useradd", "testuser"})
+		exec2.WaitWithDefaultTimeout()
+		Expect(exec2.ExitCode()).To(Equal(0))
+	})
+
 	It("podman --userns=auto", func() {
 		u, err := user.Current()
 		Expect(err).To(BeNil())