Re: [RFC PATCH] SUNRPC: Fix UAF in svc_tcp_listen_data_ready()
From: Ding Hui
Date: Mon May 08 2023 - 02:29:34 EST
On 2023/5/8 12:00, Chuck Lever III wrote:
On May 7, 2023, at 6:32 PM, Ding Hui <dinghui@xxxxxxxxxxxxxx> wrote:
On 2023/5/7 23:26, Chuck Lever III wrote:
On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@xxxxxxxxxxxxxx> wrote:
After the listener svc_sock freed, and before invoking svc_tcp_accept()
for the established child sock, there is a window that the newsock
retaining a freed listener svc_sock in sk_user_data which cloning from
parent. In the race windows if data is received on the newsock, we will
observe use-after-free report in svc_tcp_listen_data_ready().
My thought is that not calling sk_odata() for the newsock
could potentially result in missing a data_ready event,
resulting in a hung client on that socket.
I checked the vmcore, found that sk_odata points to sock_def_readable(),
and the sk_wq of newsock is NULL, which be assigned by sk_clone_lock()
unconditionally.
Calling sk_odata() for the newsock maybe do not wake up any sleepers.
IMO the preferred approach is to ensure that svsk is always
safe to dereference in tcp_listen_data_ready. I haven't yet
thought carefully about how to do that.
Agree, but I don't have a good way for now.
Would a smartly-placed svc_xprt_get() hold the listener in place
until accept processing completes?
It is difficult and complicated to me. I think it's a little bit out of
SUNRPC's control for the newsocks before accepted, e.g.: we don't know
how many they have.
Back to this RFC, I checked the code and thought it is safe by skipping
sk_odata() for the newsocks before accepted in **svc_tcp_listen_data_ready()**,
since these newsocks's sk_wq must be NULL, and will be assigned new one in
sock_alloc_inode() called by kernel_accept(), so we can say if the child sock
is not be accepted, there is nothing to be waked up.
Reproduce by two tasks:
...
--
Thanks,
- Ding Hui