Allow mounts to propagate into 9p device jail

Allow mounts from the parent namespace to propagate into the mount
namespace of the 9p device process.

BUG=none
TEST=none

Change-Id: Iff455c8967949bd3e0f2990c947d45bbbc541d45
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2018305
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Stephen Barber <smbarber@chromium.org>
Tested-by: Yusuke Sato <yusukes@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Tested-by: Chirantan Ekbote <chirantan@chromium.org>
Commit-Queue: Chirantan Ekbote <chirantan@chromium.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/linux.rs b/src/linux.rs
index a26e7bb..84edf5c 100644
--- a/src/linux.rs
+++ b/src/linux.rs
@@ -825,6 +825,10 @@ fn create_9p_device(cfg: &Config, src: &Path, tag: &str) -> DeviceResult {
             let root = Path::new("/");
             jail.mount_bind(src, root, true)?;
 
+            // We want bind mounts from the parent namespaces to propagate into the 9p server's
+            // namespace.
+            jail.set_remount_mode(libc::MS_SLAVE);
+
             add_crosvm_user_to_jail(&mut jail, "p9")?;
             (Some(jail), root)
         }