fanotify: userspace interface for permission responses

fanotify groups need to respond to events which include permissions types.
To do so groups will send a response using write() on the fanotify_fd they
have open.

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

1 files changed, 176 insertions, 6 deletions

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 09d9bdb62af3..87f0be852f71 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -18,6 +18,13 @@
 extern const struct fsnotify_ops fanotify_fsnotify_ops;
 
 static struct kmem_cache *fanotify_mark_cache __read_mostly;
+static struct kmem_cache *fanotify_response_event_cache __read_mostly;
+
+struct fanotify_response_event {
+        struct list_head list;
+        __s32 fd;
+        struct fsnotify_event *event;
+};
 
 /*
  * Get an fsnotify notification event if one exists and is small
@@ -110,23 +117,152 @@ static ssize_t fill_event_metadata(struct fsnotify_group *group,
         return metadata->fd;
 }
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+static struct fanotify_response_event *dequeue_re(struct fsnotify_group *group,
+                                                  __s32 fd)
+{
+        struct fanotify_response_event *re, *return_re = NULL;
+
+        mutex_lock(&group->fanotify_data.access_mutex);
+        list_for_each_entry(re, &group->fanotify_data.access_list, list) {
+                if (re->fd != fd)
+                        continue;
+
+                list_del_init(&re->list);
+                return_re = re;
+                break;
+        }
+        mutex_unlock(&group->fanotify_data.access_mutex);
+
+        pr_debug("%s: found return_re=%p\n", __func__, return_re);
+
+        return return_re;
+}
+
+static int process_access_response(struct fsnotify_group *group,
+                                   struct fanotify_response *response_struct)
+{
+        struct fanotify_response_event *re;
+        __s32 fd = response_struct->fd;
+        __u32 response = response_struct->response;
+
+        pr_debug("%s: group=%p fd=%d response=%d\n", __func__, group,
+                 fd, response);
+        /*
+         * make sure the response is valid, if invalid we do nothing and either
+         * userspace can send a valid responce or we will clean it up after the
+         * timeout
+         */
+        switch (response) {
+        case FAN_ALLOW:
+        case FAN_DENY:
+                break;
+        default:
+                return -EINVAL;
+        }
+
+        if (fd < 0)
+                return -EINVAL;
+
+        re = dequeue_re(group, fd);
+        if (!re)
+                return -ENOENT;
+
+        re->event->response = response;
+
+        wake_up(&group->fanotify_data.access_waitq);
+
+        kmem_cache_free(fanotify_response_event_cache, re);
+
+        return 0;
+}
+
+static int prepare_for_access_response(struct fsnotify_group *group,
+                                       struct fsnotify_event *event,
+                                       __s32 fd)
+{
+        struct fanotify_response_event *re;
+
+        if (!(event->mask & FAN_ALL_PERM_EVENTS))
+                return 0;
+
+        re = kmem_cache_alloc(fanotify_response_event_cache, GFP_KERNEL);
+        if (!re)
+                return -ENOMEM;
+
+        re->event = event;
+        re->fd = fd;
+
+        mutex_lock(&group->fanotify_data.access_mutex);
+        list_add_tail(&re->list, &group->fanotify_data.access_list);
+        mutex_unlock(&group->fanotify_data.access_mutex);
+
+        return 0;
+}
+
+static void remove_access_response(struct fsnotify_group *group,
+                                   struct fsnotify_event *event,
+                                   __s32 fd)
+{
+        struct fanotify_response_event *re;
+
+        if (!(event->mask & FAN_ALL_PERM_EVENTS))
+                return;
+
+        re = dequeue_re(group, fd);
+        if (!re)
+                return;
+
+        BUG_ON(re->event != event);
+
+        kmem_cache_free(fanotify_response_event_cache, re);
+
+        return;
+}
+#else
+static int prepare_for_access_response(struct fsnotify_group *group,
+                                       struct fsnotify_event *event,
+                                       __s32 fd)
+{
+        return 0;
+}
+
+static void remove_access_response(struct fsnotify_group *group,
+                                   struct fsnotify_event *event,
+                                   __s32 fd)
+{
+        return 0;
+}
+#endif
+
 static ssize_t copy_event_to_user(struct fsnotify_group *group,
                                   struct fsnotify_event *event,
                                   char __user *buf)
 {
         struct fanotify_event_metadata fanotify_event_metadata;
-        int ret;
+        int fd, ret;
 
         pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-        ret = fill_event_metadata(group, &fanotify_event_metadata, event);
-        if (ret < 0)
-                return ret;
+        fd = fill_event_metadata(group, &fanotify_event_metadata, event);
+        if (fd < 0)
+                return fd;
+
+        ret = prepare_for_access_response(group, event, fd);
+        if (ret)
+                goto out_close_fd;
 
+        ret = -EFAULT;
         if (copy_to_user(buf, &fanotify_event_metadata, FAN_EVENT_METADATA_LEN))
-                return -EFAULT;
+                goto out_kill_access_response;
 
         return FAN_EVENT_METADATA_LEN;
+
+out_kill_access_response:
+        remove_access_response(group, event, fd);
+out_close_fd:
+        sys_close(fd);
+        return ret;
 }
 
 /* intofiy userspace file descriptor functions */
@@ -197,6 +333,33 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
         return ret;
 }
 
+static ssize_t fanotify_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
+{
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        struct fanotify_response response = { .fd = -1, .response = -1 };
+        struct fsnotify_group *group;
+        int ret;
+
+        group = file->private_data;
+
+        if (count > sizeof(response))
+                count = sizeof(response);
+
+        pr_debug("%s: group=%p count=%zu\n", __func__, group, count);
+
+        if (copy_from_user(&response, buf, count))
+                return -EFAULT;
+
+        ret = process_access_response(group, &response);
+        if (ret < 0)
+                count = ret;
+
+        return count;
+#else
+        return -EINVAL;
+#endif
+}
+
 static int fanotify_release(struct inode *ignored, struct file *file)
 {
         struct fsnotify_group *group = file->private_data;
@@ -237,6 +400,7 @@ static long fanotify_ioctl(struct file *file, unsigned int cmd, unsigned long ar
 static const struct file_operations fanotify_fops = {
         .poll           = fanotify_poll,
         .read           = fanotify_read,
+        .write          = fanotify_write,
         .fasync         = NULL,
         .release        = fanotify_release,
         .unlocked_ioctl = fanotify_ioctl,
@@ -470,7 +634,7 @@ SYSCALL_DEFINE3(fanotify_init, unsigned int, flags, unsigned int, event_f_flags,
         if (flags & ~FAN_ALL_INIT_FLAGS)
                 return -EINVAL;
 
-        f_flags = (O_RDONLY | FMODE_NONOTIFY);
+        f_flags = O_RDWR | FMODE_NONOTIFY;
         if (flags & FAN_CLOEXEC)
                 f_flags |= O_CLOEXEC;
         if (flags & FAN_NONBLOCK)
@@ -527,7 +691,11 @@ SYSCALL_DEFINE(fanotify_mark)(int fanotify_fd, unsigned int flags,
         default:
                 return -EINVAL;
         }
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        if (mask & ~(FAN_ALL_EVENTS | FAN_ALL_PERM_EVENTS | FAN_EVENT_ON_CHILD))
+#else
         if (mask & ~(FAN_ALL_EVENTS | FAN_EVENT_ON_CHILD))
+#endif
                 return -EINVAL;
 
         filp = fget_light(fanotify_fd, &fput_needed);
@@ -600,6 +768,8 @@ SYSCALL_ALIAS(sys_fanotify_mark, SyS_fanotify_mark);
 static int __init fanotify_user_setup(void)
 {
         fanotify_mark_cache = KMEM_CACHE(fsnotify_mark, SLAB_PANIC);
+        fanotify_response_event_cache = KMEM_CACHE(fanotify_response_event,
+                                                   SLAB_PANIC);
 
         return 0;
 }