fix: contain file-explorer binds into Sencho's system directories (#1484)

The file-explorer root containment treated only kernel and OS-state paths
(/etc, /proc, /sys, /dev, /run, /var/run) as dangerous. System locations
that hold the executables and libraries Sencho's own runtime depends on,
notably /usr (which contains /usr/local/bin/node, the docker CLI, and the
entrypoint) plus /bin, /sbin, /lib, /lib64, /boot and /root, were left
browsable, writable and chmodable.

A stack author with stack:edit could declare one of these as a bind source,
overwrite a binary, and have a later deploy execute it. Add those locations
to the dangerous-root set so such a bind is never browsable or editable; the
boundary check still permits ordinary host paths whose name merely prefixes a
protected root (for example /usrdata).

backend/src/__tests__/stack-file-roots-service.test.ts

@@ -67,12 +67,18 @@ afterEach(async () => {
 
 describe('isDangerousHostPath', () => {
   it('flags the root and protected system directories and their descendants', () => {
-    for (const p of ['/', '/etc', '/etc/nginx', '/proc', '/sys/x', '/dev/sda', '/var/run', '/var/run/docker.sock', '/run/x']) {
+    for (const p of [
+      '/', '/etc', '/etc/nginx', '/proc', '/sys/x', '/dev/sda', '/var/run', '/var/run/docker.sock', '/run/x',
+      // System locations holding the executables/libraries Sencho's runtime
+      // depends on: a bind here could overwrite a binary a deploy later runs.
+      '/usr', '/usr/local/bin', '/usr/local/bin/node', '/usr/bin', '/usr/lib', '/bin', '/bin/sh',
+      '/sbin', '/lib', '/lib64', '/boot', '/root', '/root/.ssh',
+    ]) {
       expect(isDangerousHostPath(p)).toBe(true);
     }
   });
-  it('allows ordinary host paths', () => {
-    for (const p of ['/home/user/config', '/srv/app/data', 'C:\\data', '/etcetera']) {
+  it('allows ordinary host paths, including ones whose name only prefixes a protected root', () => {
+    for (const p of ['/home/user/config', '/srv/app/data', '/opt/app', '/mnt/data', 'C:\\data', '/etcetera', '/usrdata', '/libreoffice', '/booted']) {
       expect(isDangerousHostPath(p)).toBe(false);
     }
   });
@@ -154,6 +160,20 @@ describe('StackFileRootsService.listRoots', () => {
     expect(bind?.browsable).toBe(false);
   });
 
+  it('blocks a bind into a system binary directory (/usr/local/bin) so Sencho binaries cannot be overwritten', async () => {
+    // A stack author with stack:edit could otherwise declare /usr/local/bin as a
+    // bind source, overwrite node/docker/the entrypoint, and have a later deploy
+    // execute it. The declared source is dangerous regardless of how realpath
+    // rewrites it (covered by the dangerousSource term), so this holds on any host.
+    stub({ rendered: renderModel({ web: [{ type: 'bind', source: '/usr/local/bin', target: '/host-bin', read_only: false }] }) });
+    const roots = await StackFileRootsService.getInstance(1).listRoots(STACK, { fresh: true });
+    const bind = roots.find((r) => r.kind === 'bind');
+    expect(bind?.dangerous).toBe(true);
+    expect(bind?.browsable).toBe(false);
+    expect(bind?.writable).toBe(false);
+    expect(bind?.chmodable).toBe(false);
+  });
+
   it('blocks a dangerous declared source even when realpath rewrites it to a benign canonical', async () => {
     // Guards the dangerousSource term: realpath can rewrite a dangerous POSIX
     // source to a benign-looking canonical (a non-existent POSIX path resolves

backend/src/services/StackFileRootsService.ts

@@ -105,9 +105,20 @@ export function stackSourceFileRoot(hostPathOrName = ''): StackFileRoot {
 const ROOTS_CACHE_TTL_MS = 15_000;
 
 // Dangerous host directories: a bind equal to or under any of these grants
-// node-level access and is never browsable. The docker socket is caught
-// separately via isDockerSocketMount on the declared source.
-const DANGEROUS_ROOTS = ['/etc', '/proc', '/sys', '/dev', '/var/run', '/run'];
+// node-level access and is never browsable. Two groups:
+//   - kernel/OS state: /etc, /proc, /sys, /dev, /var/run, /run.
+//   - the system locations holding the executables and libraries Sencho's own
+//     runtime depends on: /usr (which contains /usr/local/bin/{node,docker,npm}
+//     and /usr/local/lib), /bin, /sbin, /lib, /lib64 (the base-image binaries),
+//     plus /boot and /root. A stack author with stack:edit must not be able to
+//     declare one of these as a bind source, overwrite a binary, and have a
+//     later deploy execute it.
+// The docker socket is caught separately via isDockerSocketMount on the
+// declared source.
+const DANGEROUS_ROOTS = [
+  '/etc', '/proc', '/sys', '/dev', '/var/run', '/run',
+  '/usr', '/bin', '/sbin', '/lib', '/lib64', '/boot', '/root',
+];
 
 interface CacheEntry {
   roots: StackFileRoot[];