syscall: skip non-root user namespace test if kernel forbids

The unprivileged_userns_clone sysctl prevents unpriviledged users from
creating namespaces, which the AmbientCaps test does. It's set to 0 by
default in a few Linux distributions (Debian and Arch, possibly
others), so we need to check it before running the test.

I've verified that setting

  echo 1 > /proc/sys/kernel/unprivileged_userns_clone

and then running the test *without this patch* makes it pass, which
proves that checking unprivileged_userns_clone is indeed sufficient.

Fixes #30698

Change-Id: Ib2079b5e714d7f2440ddf979c3e7cfda9a9c5005
Reviewed-on: https://go-review.googlesource.com/c/go/+/166460
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/syscall/exec_linux_test.go b/src/syscall/exec_linux_test.go
index dc16a9d9fe440fc1378e54fe56dba5512df38c12..826487b676bbff40ee31282d8265b97507d326d8 100644 (file)
--- a/src/syscall/exec_linux_test.go
+++ b/src/syscall/exec_linux_test.go
@@ -539,6 +539,13 @@ func testAmbientCaps(t *testing.T, userns bool) {
                t.Skip("skipping test on Kubernetes-based builders; see Issue 12815")
        }
 
+       // Skip the test if the sysctl that prevents unprivileged user
+       // from creating user namespaces is enabled.
+       data, errRead := ioutil.ReadFile("/proc/sys/kernel/unprivileged_userns_clone")
+       if errRead == nil && data[0] == '0' {
+               t.Skip("kernel prohibits user namespace in unprivileged process")
+       }
+
        // skip on android, due to lack of lookup support
        if runtime.GOOS == "android" {
                t.Skip("skipping test on android; see Issue 27327")