fanotify: sanitize failure exits in copy_event_to_user()

* do copy_to_user() before prepare_for_access_response(); that kills
the need in remove_access_response().
* don't do fd_install() until we are past the last possible failure
exit.  Don't use sys_close() on cleanup side - just put_unused_fd()
and fput().  Less racy that way...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index d438036..ea48693 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -58,7 +58,9 @@ static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
        return fsnotify_remove_notify_event(group);
 }
 
-static int create_fd(struct fsnotify_group *group, struct fsnotify_event *event)
+static int create_fd(struct fsnotify_group *group,
+                       struct fsnotify_event *event,
+                       struct file **file)
 {
        int client_fd;
        struct file *new_file;
@@ -98,7 +100,7 @@ static int create_fd(struct fsnotify_group *group, struct fsnotify_event *event)
                put_unused_fd(client_fd);
                client_fd = PTR_ERR(new_file);
        } else {
-               fd_install(client_fd, new_file);
+               *file = new_file;
        }
 
        return client_fd;
@@ -106,13 +108,15 @@ static int create_fd(struct fsnotify_group *group, struct fsnotify_event *event)
 
 static int fill_event_metadata(struct fsnotify_group *group,
                                   struct fanotify_event_metadata *metadata,
-                                  struct fsnotify_event *event)
+                                  struct fsnotify_event *event,
+                                  struct file **file)
 {
        int ret = 0;
 
        pr_debug("%s: group=%p metadata=%p event=%p\n", __func__,
                 group, metadata, event);
 
+       *file = NULL;
        metadata->event_len = FAN_EVENT_METADATA_LEN;
        metadata->metadata_len = FAN_EVENT_METADATA_LEN;
        metadata->vers = FANOTIFY_METADATA_VERSION;
@@ -121,7 +125,7 @@ static int fill_event_metadata(struct fsnotify_group *group,
        if (unlikely(event->mask & FAN_Q_OVERFLOW))
                metadata->fd = FAN_NOFD;
        else {
-               metadata->fd = create_fd(group, event);
+               metadata->fd = create_fd(group, event, file);
                if (metadata->fd < 0)
                        ret = metadata->fd;
        }
@@ -220,25 +224,6 @@ static int prepare_for_access_response(struct fsnotify_group *group,
        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,
@@ -247,12 +232,6 @@ static int prepare_for_access_response(struct fsnotify_group *group,
        return 0;
 }
 
-static void remove_access_response(struct fsnotify_group *group,
-                                  struct fsnotify_event *event,
-                                  __s32 fd)
-{
-       return;
-}
 #endif
 
 static ssize_t copy_event_to_user(struct fsnotify_group *group,
@@ -260,31 +239,33 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
                                  char __user *buf)
 {
        struct fanotify_event_metadata fanotify_event_metadata;
+       struct file *f;
        int fd, ret;
 
        pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-       ret = fill_event_metadata(group, &fanotify_event_metadata, event);
+       ret = fill_event_metadata(group, &fanotify_event_metadata, event, &f);
        if (ret < 0)
                goto out;
 
        fd = fanotify_event_metadata.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,
                         fanotify_event_metadata.event_len))
-               goto out_kill_access_response;
+               goto out_close_fd;
+
+       ret = prepare_for_access_response(group, event, fd);
+       if (ret)
+               goto out_close_fd;
 
+       fd_install(fd, f);
        return fanotify_event_metadata.event_len;
 
-out_kill_access_response:
-       remove_access_response(group, event, fd);
 out_close_fd:
-       if (fd != FAN_NOFD)
-               sys_close(fd);
+       if (fd != FAN_NOFD) {
+               put_unused_fd(fd);
+               fput(f);
+       }
 out:
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
        if (event->mask & FAN_ALL_PERM_EVENTS) {