From 38480ce6c63460cf485f49605df9458a269dac57 Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Thu, 21 Mar 2024 16:11:22 -0400
Subject: [PATCH] install: Verify userns for /proc/1 early on

This will catch rootless podman cases even more reliably (assuming
we were invoked with `--pid=host`).

Signed-off-by: Colin Walters <walters@verbum.org>
---
 lib/src/containerenv.rs |  2 +-
 lib/src/install.rs      | 38 ++++++++++++++++++++++++++++++++------
 2 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/lib/src/containerenv.rs b/lib/src/containerenv.rs
index 2e9ffcb46..71e0e0899 100644
--- a/lib/src/containerenv.rs
+++ b/lib/src/containerenv.rs
@@ -8,7 +8,7 @@ use cap_std_ext::prelude::CapStdExtDirExt;
 use fn_error_context::context;
 
 /// Path is relative to container rootfs (assumed to be /)
-const PATH: &str = "run/.containerenv";
+pub(crate) const PATH: &str = "run/.containerenv";
 
 #[derive(Debug, Default)]
 pub(crate) struct ContainerExecutionInfo {
diff --git a/lib/src/install.rs b/lib/src/install.rs
index 50b1a65eb..336fc9b89 100644
--- a/lib/src/install.rs
+++ b/lib/src/install.rs
@@ -28,7 +28,7 @@ use cap_std_ext::prelude::CapStdExtDirExt;
 use chrono::prelude::*;
 use clap::ValueEnum;
 use ostree_ext::oci_spec;
-use rustix::fs::FileTypeExt;
+use rustix::fs::{FileTypeExt, MetadataExt as _};
 
 use fn_error_context::context;
 use ostree::gio;
@@ -848,8 +848,8 @@ pub(crate) fn finalize_filesystem(fs: &Utf8Path) -> Result<()> {
     Ok(())
 }
 
+/// A heuristic check that we were invoked with --pid=host
 fn require_host_pidns() -> Result<()> {
-    // We require --pid=host
     if rustix::process::getpid().is_init() {
         anyhow::bail!("This command must be run with --pid=host")
     }
@@ -857,6 +857,23 @@ fn require_host_pidns() -> Result<()> {
     Ok(())
 }
 
+/// Verify that we can access /proc/1, which will catch rootless podman (with --pid=host)
+/// for example.
+fn require_host_userns() -> Result<()> {
+    let proc1 = "/proc/1";
+    let pid1_uid = Path::new(proc1)
+        .metadata()
+        .with_context(|| format!("Querying {proc1}"))?
+        .uid();
+    // We must really be in a rootless container, or in some way
+    // we're not part of the host user namespace.
+    if pid1_uid != 0 {
+        anyhow::bail!("{proc1} is owned by {pid1_uid}, not zero; this command must be run in the root user namespace (e.g. not rootless podman)");
+    }
+    tracing::trace!("OK: we're in a matching user namespace with pid1");
+    Ok(())
+}
+
 // Ensure the `/var` directory exists.
 fn ensure_var() -> Result<()> {
     std::fs::create_dir_all("/var")?;
@@ -996,13 +1013,22 @@ async fn prepare_install(
     let external_source = source_opts.source_imgref.is_some();
     let source = match source_opts.source_imgref {
         None => {
+            // Out of conservatism we only verify the host userns path when we're expecting
+            // to do a self-install (e.g. not bootc-image-builder or equivalent).
+            require_host_userns()?;
             let container_info = crate::containerenv::get_container_execution_info(&rootfs)?;
             // This command currently *must* be run inside a privileged container.
-            if let Some("1") = container_info.rootless.as_deref() {
-                anyhow::bail!(
+            match container_info.rootless.as_deref() {
+                Some("1") => anyhow::bail!(
                     "Cannot install from rootless podman; this command must be run as root"
-                );
-            }
+                ),
+                Some(o) => tracing::debug!("rootless={o}"),
+                // This one shouldn't happen except on old podman
+                None => tracing::debug!(
+                    "notice: Did not find rootless= entry in {}",
+                    crate::containerenv::PATH,
+                ),
+            };
             tracing::trace!("Read container engine info {:?}", container_info);
 
             SourceInfo::from_container(&container_info)?