Re: Crash due to destroying TCP request sockets using SOCK_DESTROY

On 07/05/2018 09:46 PM, Lorenzo Colitti wrote:

On Fri, Jul 6, 2018 at 11:37 AM Subash Abhinov Kasiviswanathan
[off-list ref] wrote:

quoted

 From the call stack, a TCP socket is being destroyed using netlink_diag.
The memory dump showed that the socket was an inet request socket (in
state TCP_NEW_SYN_RECV) with refcount of 0.
[...]
  13232.479820:   <2> refcount_t: underflow; use-after-free.
  13232.479838:   <6> ------------[ cut here ]------------
  13232.479843:   <6> kernel BUG at kernel/msm-4.14/lib/refcount.c:204!
  13232.479849:   <6> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[...]
  13232.479996:   <6> Process netd (pid: 648, stack limit =
0xffffff801cf98000)
  13232.479998:   <2> Call trace:
  13232.480000:   <2>  refcount_sub_and_test+0x64/0x78
  13232.480002:   <2>  refcount_dec_and_test+0x18/0x24
  13232.480005:   <2>  sock_gen_put+0x1c/0xb0
  13232.480009:   <2>  tcp_diag_destroy+0x54/0x68
[...]

Looks like for a TCP_NEW_SYN_RECV socket, sock_diag_destroy
essentially ends up doing:

                        struct request_sock *req = inet_reqsk(sk);

                        local_bh_disable();
                        inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
                                                          req);
                        local_bh_enable();
...

        sock_gen_put(sk);

It looks like inet_csk_reqsk_queue_drop_and_put calls reqsk_put(req),
which frees the socket, and at that point sock_gen_put is a UAF. Do we
just need:

-                        inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
-                                                           req);
+                        inet_csk_reqsk_queue_drop(req->rsk_listener, req);

since sock_gen_put will also end up calling reqsk_put() for a
TCP_SYN_RECV socket?

Alastair - you're able to reproduce this UAF using net_test on qemu,
right? If so, could you try that two-line patch above?

Hi Lorenzo

Your patch makes sense to me, please submit it formally with :

Fixes: d7226c7a4dd1 ("net: diag: Fix refcnt leak in error path destroying socket")
Cc: David Ahern <redacted>

Thanks !