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>

1 files changed, 20 insertions, 39 deletions

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index d43803669739..ea48693940f1 100644
--- 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) {