fanotify: permissions and blocking

This is the backend work needed for fanotify to support the new
FS_OPEN_PERM and FS_ACCESS_PERM fsnotify events.  This is done using the
new fsnotify secondary queue.  No userspace interface is provided actually
respond to or request these events.

Signed-off-by: Eric Paris <eparis@redhat.com>

3 files changed, 69 insertions, 4 deletions

diff --git a/fs/notify/fanotify/Kconfig b/fs/notify/fanotify/Kconfig
index 668e5df28e28..566de30395c2 100644
--- a/fs/notify/fanotify/Kconfig
+++ b/fs/notify/fanotify/Kconfig
@@ -10,3 +10,17 @@ config FANOTIFY
            the event.
 
            If unsure, say Y.
+
+config FANOTIFY_ACCESS_PERMISSIONS
+        bool "fanotify permissions checking"
+        depends on FANOTIFY
+        depends on SECURITY
+        default n
+        ---help---
+           Say Y here is you want fanotify listeners to be able to make permissions
+           decisions concerning filesystem events.  This is used by some fanotify
+           listeners which need to scan files before allowing the system access to
+           use those files.  This is used by some anti-malware vendors and by some
+           hierarchical storage managent systems.
+
+           If unsure, say N.
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 4feed8601e29..52d0a55a249e 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -2,9 +2,12 @@
 #include <linux/fdtable.h>
 #include <linux/fsnotify_backend.h>
 #include <linux/init.h>
+#include <linux/jiffies.h>
 #include <linux/kernel.h> /* UINT_MAX */
 #include <linux/mount.h>
+#include <linux/sched.h>
 #include <linux/types.h>
+#include <linux/wait.h>
 
 static bool should_merge(struct fsnotify_event *old, struct fsnotify_event *new)
 {
@@ -88,10 +91,37 @@ out:
         return ret;
 }
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+static int fanotify_get_response_from_access(struct fsnotify_group *group,
+                                             struct fsnotify_event *event)
+{
+        int ret;
+
+        pr_debug("%s: group=%p event=%p\n", __func__, group, event);
+
+        wait_event(group->fanotify_data.access_waitq, event->response);
+
+        /* userspace responded, convert to something usable */
+        spin_lock(&event->lock);
+        switch (event->response) {
+        case FAN_ALLOW:
+                ret = 0;
+                break;
+        case FAN_DENY:
+        default:
+                ret = -EPERM;
+        }
+        event->response = 0;
+        spin_unlock(&event->lock);
+
+        return ret;
+}
+#endif
+
 static int fanotify_handle_event(struct fsnotify_group *group, struct fsnotify_event *event)
 {
         int ret;
-        struct fsnotify_event *used_event;
+        struct fsnotify_event *notify_event = NULL;
 
         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
@@ -100,15 +130,31 @@ static int fanotify_handle_event(struct fsnotify_group *group, struct fsnotify_e
         BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
         BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
         BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
+        BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
+        BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
 
         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-        ret = fsnotify_add_notify_event(group, event, NULL, fanotify_merge, (void **)&used_event);
+        ret = fsnotify_add_notify_event(group, event, NULL, fanotify_merge,
+                                        (void **)&notify_event);
         /* -EEXIST means this event was merged with another, not that it was an error */
         if (ret == -EEXIST)
                 ret = 0;
-        if (used_event)
-                fsnotify_put_event(used_event);
+        if (ret)
+                goto out;
+
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        if (event->mask & FAN_ALL_PERM_EVENTS) {
+                /* if we merged we need to wait on the new event */
+                if (notify_event)
+                        event = notify_event;
+                ret = fanotify_get_response_from_access(group, event);
+        }
+#endif
+
+out:
+        if (notify_event)
+                fsnotify_put_event(notify_event);
         return ret;
 }
 
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 84d3e2047de3..09d9bdb62af3 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -482,6 +482,11 @@ SYSCALL_DEFINE3(fanotify_init, unsigned int, flags, unsigned int, event_f_flags,
                 return PTR_ERR(group);
 
         group->priority = priority;
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        mutex_init(&group->fanotify_data.access_mutex);
+        init_waitqueue_head(&group->fanotify_data.access_waitq);
+        INIT_LIST_HEAD(&group->fanotify_data.access_list);
+#endif
 
         fd = anon_inode_getfd("[fanotify]", &fanotify_fops, group, f_flags);
         if (fd < 0)