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>

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 52d0a55..bbcfccd 100644 (file)
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -114,6 +114,9 @@ static int fanotify_get_response_from_access(struct fsnotify_group *group,
        event->response = 0;
        spin_unlock(&event->lock);
 
+       pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
+                group, event, ret);
+       
        return ret;
 }
 #endif

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 09d9bdb..87f0be8 100644 (file)
--- 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;
 }

diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 02f8067..f0949a5 100644 (file)
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -75,6 +75,11 @@ struct fanotify_event_metadata {
        __s64 pid;
 } __attribute__ ((packed));
 
+struct fanotify_response {
+       __s32 fd;
+       __u32 response;
+} __attribute__ ((packed));
+
 /* Legit userspace responses to a _PERM event */
 #define FAN_ALLOW      0x01
 #define FAN_DENY       0x02