On Thu, Oct 19, 2017 at 4:58 PM, Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
> 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.
Interesting.
Because all marks are ordered by group priority and there are no permission
events in priority 0, as soon as we see group prio 0 on both inode and vfs mark,
we can maybe change the mark iteration?
>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> Fixes: 05f0e38724e8 ("fanotify: Release SRCU lock when waiting for userspace response")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.12
> ---
> fs/notify/fanotify/fanotify.c | 33 ++++++++++++++++++++-------------
> 1 file changed, 20 insertions(+), 13 deletions(-)
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 2fa99aeaa095..fb7a1339982c 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -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
Well you are not the one to introduce ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
to this code, but I have to wonder, what are all those ifdefs doing in
this code?
What are they trying to save?
FAN_ALL_PERM_EVENTS is masked out from valid event flags in fanotify_mark()
I don't really see a reason for any other ifdef in non headers here.
> +
> 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;
> }
> --
> 2.5.5
>
