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Subject[PATCH 4.14 063/193] fanotify: fix fsnotify_prepare_user_wait() failure
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@redhat.com>

commit f37650f1c7c71cf5180b43229d13b421d81e7170 upstream.

If fsnotify_prepare_user_wait() fails, we leave the event on the
notification list. Which will result in a warning in
fsnotify_destroy_event() and later use-after-free.

Instead of adding a new helper to remove the event from the list in this
case, I opted to move the prepare/finish up into fanotify_handle_event().

This will allow these to be moved further out into the generic code later,
and perhaps let us move to non-sleeping RCU.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 05f0e38724e8 ("fanotify: Release SRCU lock when waiting for userspace response")
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/notify/fanotify/fanotify.c | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)

--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -65,19 +65,8 @@ static int fanotify_get_response(struct

pr_debug("%s: group=%p event=%p\n", __func__, group, event);

- /*
- * fsnotify_prepare_user_wait() fails if we race with mark deletion.
- * Just let the operation pass in that case.
- */
- if (!fsnotify_prepare_user_wait(iter_info)) {
- event->response = FAN_ALLOW;
- goto out;
- }
-
wait_event(group->fanotify_data.access_waitq, event->response);

- fsnotify_finish_user_wait(iter_info);
-out:
/* userspace responded, convert to something usable */
switch (event->response) {
case FAN_ALLOW:
@@ -212,9 +201,21 @@ static int fanotify_handle_event(struct
pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
mask);

+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+ if (mask & FAN_ALL_PERM_EVENTS) {
+ /*
+ * fsnotify_prepare_user_wait() fails if we race with mark
+ * deletion. Just let the operation pass in that case.
+ */
+ if (!fsnotify_prepare_user_wait(iter_info))
+ return 0;
+ }
+#endif
+
event = fanotify_alloc_event(inode, mask, data);
+ ret = -ENOMEM;
if (unlikely(!event))
- return -ENOMEM;
+ goto finish;

fsn_event = &event->fse;
ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
@@ -224,7 +225,8 @@ static int fanotify_handle_event(struct
/* Our event wasn't used in the end. Free it. */
fsnotify_destroy_event(group, fsn_event);

- return 0;
+ ret = 0;
+ goto finish;
}

#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
@@ -233,6 +235,11 @@ static int fanotify_handle_event(struct
iter_info);
fsnotify_destroy_event(group, fsn_event);
}
+finish:
+ if (mask & FAN_ALL_PERM_EVENTS)
+ fsnotify_finish_user_wait(iter_info);
+#else
+finish:
#endif
return ret;
}

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