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fanotify: fix fsnotify_prepare_user_wait() failure 

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: 05f0e38724 ("fanotify: Release SRCU lock when waiting for userspace response")
Cc: <stable@vger.kernel.org> # v4.12
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Miklos Szeredi 2017-10-30 21:14:56 +01:00 committed by Jan Kara
parent 9a31d7ad99
commit f37650f1c7
1 changed files with 20 additions and 13 deletions
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33
fs/notify/fanotify/fanotify.c
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@ -64,19 +64,8 @@ static int fanotify_get_response(struct fsnotify_group *group,
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:
@ -211,9 +200,21 @@ static int fanotify_handle_event(struct fsnotify_group *group,
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);
@ -223,7 +224,8 @@ static int fanotify_handle_event(struct fsnotify_group *group,
/* 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
@ -232,6 +234,11 @@ static int fanotify_handle_event(struct fsnotify_group *group,
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;
}