Set PATH unconditionally even if mount namespace is set up

spread-tests/regression/lp-1630479/task.yaml

@@ -0,0 +1,21 @@
+summary: Regression check for https://bugs.launchpad.net/snap-confine/+bug/1630479
+details: |
+    The PATH environment variable needs to make sense for the layout of the
+    core snap. Snap-confine contains code that sets it accordingly but during
+    the introduction of the namespace sharing feature that code would run only
+    when the namespace was initially constructed. Subsequent calls would not
+    see the correct path. 
+prepare: |
+    echo "Having installed the snapd-hacker-toolbelt snap"
+    snap install snapd-hacker-toolbelt
+execute: |
+    echo "We can observe the value of PATH twice"
+    revision=$(readlink /snap/snapd-hacker-toolbelt/current)
+    one="$(snapd-hacker-toolbelt.busybox sh -c 'echo $PATH')"
+    two="$(snapd-hacker-toolbelt.busybox sh -c 'echo $PATH')"
+    echo "We can see that PATH is stable across calls"
+    [ "$one" = "$two" ]
+    echo "We can make sure that it has the right value"
+    [ "$one" = "/snap/snapd-hacker-toolbelt/$revision/bin:/snap/snapd-hacker-toolbelt/$revision/usr/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games" ]
+restore: |
+    snap remove snapd-hacker-toolbelt

src/mount-support.c

@@ -349,13 +349,6 @@ static void setup_snappy_os_mounts()
 	sc_bind_mount_hostfs(rootfs_dir);
 	sc_mount_nvidia_driver(rootfs_dir);
 	sc_pivot_to_new_rootfs(rootfs_dir);
-	// Reset path as we cannot rely on the path from the host OS to
-	// make sense. The classic distribution may use any PATH that makes
-	// sense but we cannot assume it makes sense for the core snap
-	// layout. Note that the /usr/local directories are explicitly
-	// left out as they are not part of the core snap.
-	debug("resetting PATH to values in sync with core snap");
-	setenv("PATH", "/usr/sbin:/usr/bin:/sbin:/bin:/usr/games", 1);
 }
 
 /**

src/sc-main.c

@@ -97,6 +97,13 @@ int sc_main(int argc, char **argv)
 		}
 		sc_unlock_ns_mutex(group);
 		sc_close_ns_group(group);
+		// Reset path as we cannot rely on the path from the host OS to
+		// make sense. The classic distribution may use any PATH that makes
+		// sense but we cannot assume it makes sense for the core snap
+		// layout. Note that the /usr/local directories are explicitly
+		// left out as they are not part of the core snap.
+		debug("resetting PATH to values in sync with core snap");
+		setenv("PATH", "/usr/sbin:/usr/bin:/sbin:/bin:/usr/games", 1);
 		struct snappy_udev udev_s;
 		if (snappy_udev_init(security_tag, &udev_s) == 0)
 			setup_devices_cgroup(security_tag, &udev_s);