On Fri, Jul 6, 2018 at 11:37 AM Subash Abhinov Kasiviswanathan
<subas...@codeaurora.org> wrote:
>
> 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?
