homed: keep "pinning" fd open while home dir active

The pin fd keeps the mount busy, ensuring that unmount requests need to
go through us.

Note that this doesn't change too much IRL, since a logged in user
generally has processes keeping the home dir busy anyway. However, in
some corner cases it is safer to protect from accidental unmounts this
way. (e.g. if user manually called "homectl activate" first).

diff --git a/src/home/homed-home.c b/src/home/homed-home.c
index bbdc6940f3da0f0db4e0fc3a871655233eb98d01..41f8ea1299ffc72cd80d0d878a1327bb6a2b3d45 100644 (file)
--- a/src/home/homed-home.c
+++ b/src/home/homed-home.c
@@ -130,6 +130,7 @@ int home_new(Manager *m, UserRecord *hr, const char *sysfs, Home **ret) {
                 .worker_stdout_fd = -1,
                 .sysfs = TAKE_PTR(ns),
                 .signed_locally = -1,
+                .pin_fd = -1,
         };
 
         r = hashmap_put(m->homes_by_name, home->user_name, home);
@@ -203,6 +204,8 @@ Home *home_free(Home *h) {
 
         h->current_operation = operation_unref(h->current_operation);
 
+        safe_close(h->pin_fd);
+
         return mfree(h);
 }
 
@@ -317,6 +320,48 @@ int home_unlink_record(Home *h) {
         return 0;
 }
 
+static void home_unpin(Home *h) {
+        assert(h);
+
+        if (h->pin_fd < 0)
+                return;
+
+        h->pin_fd = safe_close(h->pin_fd);
+        log_debug("Successfully closed pin fd on home for %s.", h->user_name);
+}
+
+static void home_pin(Home *h) {
+        const char *path;
+
+        assert(h);
+
+        if (h->pin_fd >= 0) /* Already pinned? */
+                return;
+
+        path = user_record_home_directory(h->record);
+        if (!path) {
+                log_warning("No home directory path to pin for %s, ignoring.", h->user_name);
+                return;
+        }
+
+        h->pin_fd = open(path, O_RDONLY|O_DIRECTORY|O_CLOEXEC);
+        if (h->pin_fd < 0) {
+                log_warning_errno(errno, "Couldn't open home directory '%s' for pinning, ignoring: %m", path);
+                return;
+        }
+
+        log_debug("Successfully pinned home directory '%s'.", path);
+}
+
+static void home_update_pin_fd(Home *h, HomeState state) {
+        assert(h);
+
+        if (state < 0)
+                state = home_get_state(h);
+
+        return HOME_STATE_IS_ACTIVE(state) ? home_pin(h) : home_unpin(h);
+}
+
 static void home_set_state(Home *h, HomeState state) {
         HomeState old_state, new_state;
 
@@ -331,6 +376,8 @@ static void home_set_state(Home *h, HomeState state) {
                  home_state_to_string(old_state),
                  home_state_to_string(new_state));
 
+        home_update_pin_fd(h, new_state);
+
         if (HOME_STATE_IS_EXECUTING_OPERATION(old_state) && !HOME_STATE_IS_EXECUTING_OPERATION(new_state)) {
                 /* If we just finished executing some operation, process the queue of pending operations. And
                  * enqueue it for GC too. */
@@ -1253,9 +1300,14 @@ static int home_deactivate_internal(Home *h, bool force, sd_bus_error *error) {
 
         assert(h);
 
+        home_unpin(h); /* unpin so that we can deactivate */
+
         r = home_start_work(h, force ? "deactivate-force" : "deactivate", h->record, NULL);
-        if (r < 0)
+        if (r < 0) {
+                /* Operation failed before it even started, reacquire pin fd, if state still dictates so */
+                home_update_pin_fd(h, _HOME_STATE_INVALID);
                 return r;
+        }
 
         home_set_state(h, HOME_DEACTIVATING);
         return 0;

diff --git a/src/home/homed-home.h b/src/home/homed-home.h
index 7f531a234c813ea3d2ead60cd2dd18ca36fb3287..cd3b01ba72a29f9d219e6b2409d13132db3e2db7 100644 (file)
--- a/src/home/homed-home.h
+++ b/src/home/homed-home.h
@@ -126,6 +126,9 @@ struct Home {
 
         /* Used to coalesce bus PropertiesChanged events */
         sd_event_source *deferred_change_event_source;
+
+        /* An fd to the top-level home directory we keep while logged in, to keep the dir busy */
+        int pin_fd;
 };
 
 int home_new(Manager *m, UserRecord *hr, const char *sysfs, Home **ret);