Re: [PATCH net 2/2] net/smc: fix LGR and link use-after-free issue

Wenjia Zhang
2024-11-22T15:56:45Z

On 22.11.24 08:16, Wen Gu wrote:
> We encountered a LGR/link use-after-free issue, which manifested as
> the LGR/link refcnt reaching 0 early and entering the clear process,
> making resource access unsafe.
>

How did you make sure that the refcount mentioned in the warning are the
LGR/link refcnt, not &sk->sk_refcnt?

> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 14 PID: 107447 at lib/refcount.c:25 refcount_warn_saturate+0x9c/0x140
> Workqueue: events smc_lgr_terminate_work [smc]
> Call trace:
> refcount_warn_saturate+0x9c/0x140
> __smc_lgr_terminate.part.45+0x2a8/0x370 [smc]
> smc_lgr_terminate_work+0x28/0x30 [smc]
> process_one_work+0x1b8/0x420
> worker_thread+0x158/0x510
> kthread+0x114/0x118
>
> or
>
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 6 PID: 93140 at lib/refcount.c:28 refcount_warn_saturate+0xf0/0x140
> Workqueue: smc_hs_wq smc_listen_work [smc]
> Call trace:
> refcount_warn_saturate+0xf0/0x140
> smcr_link_put+0x1cc/0x1d8 [smc]
> smc_conn_free+0x110/0x1b0 [smc]
> smc_conn_abort+0x50/0x60 [smc]
> smc_listen_find_device+0x75c/0x790 [smc]
> smc_listen_work+0x368/0x8a0 [smc]
> process_one_work+0x1b8/0x420
> worker_thread+0x158/0x510
> kthread+0x114/0x118
>
> It is caused by repeated release of LGR/link refcnt. One suspect is that
> smc_conn_free() is called repeatedly because some smc_conn_free() are not
> protected by sock lock.
>
> Calls under socklock | Calls not under socklock
> -------------------------------------------------------
> lock_sock(sk) | smc_conn_abort
> smc_conn_free | \- smc_conn_free
> \- smcr_link_put | \- smcr_link_put (duplicated)
> release_sock(sk)
>
> So make sure smc_conn_free() is called under the sock lock.
>

If I understand correctly, the fix could only solve a part of the
problem, i.e. what the second call trace reported, right?

> Fixes: 8cf3f3e42374 ("net/smc: use helper smc_conn_abort() in listen processing")
> Co-developed-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
> Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
> Co-developed-by: Kai <KaiShen@linux.alibaba.com>
> Signed-off-by: Kai <KaiShen@linux.alibaba.com>
> Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
> ---
> net/smc/af_smc.c | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index ed6d4d520bc7..e0a7a0151b11 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -973,7 +973,8 @@ static int smc_connect_decline_fallback(struct smc_sock *smc, int reason_code,
> return smc_connect_fallback(smc, reason_code);
> }
>
> -static void smc_conn_abort(struct smc_sock *smc, int local_first)
> +static void __smc_conn_abort(struct smc_sock *smc, int local_first,
> + bool locked)
> {
> struct smc_connection *conn = &smc->conn;
> struct smc_link_group *lgr = conn->lgr;
> @@ -982,11 +983,27 @@ static void smc_conn_abort(struct smc_sock *smc, int local_first)
> if (smc_conn_lgr_valid(conn))
> lgr_valid = true;
>
> - smc_conn_free(conn);
> + if (!locked) {
> + lock_sock(&smc->sk);
> + smc_conn_free(conn);
> + release_sock(&smc->sk);
> + } else {
> + smc_conn_free(conn);
> + }
> if (local_first && lgr_valid)
> smc_lgr_cleanup_early(lgr);
> }
>
> +static void smc_conn_abort(struct smc_sock *smc, int local_first)
> +{
> + __smc_conn_abort(smc, local_first, false);
> +}
> +
> +static void smc_conn_abort_locked(struct smc_sock *smc, int local_first)
> +{
> + __smc_conn_abort(smc, local_first, true);
> +}
> +
> /* check if there is a rdma device available for this connection. */
> /* called for connect and listen */
> static int smc_find_rdma_device(struct smc_sock *smc, struct smc_init_info *ini)
> @@ -1352,7 +1369,7 @@ static int smc_connect_rdma(struct smc_sock *smc,
>
> return 0;
> connect_abort:
> - smc_conn_abort(smc, ini->first_contact_local);
> + smc_conn_abort_locked(smc, ini->first_contact_local);
> mutex_unlock(&smc_client_lgr_pending);
> smc->connect_nonblock = 0;
>
> @@ -1454,7 +1471,7 @@ static int smc_connect_ism(struct smc_sock *smc,
>
> return 0;
> connect_abort:
> - smc_conn_abort(smc, ini->first_contact_local);
> + smc_conn_abort_locked(smc, ini->first_contact_local);
> mutex_unlock(&smc_server_lgr_pending);
> smc->connect_nonblock = 0;
>

Why is smc_conn_abort_locked() only necessary for the smc_connect_work,
not for the smc_listen_work?

Thanks,
Wenjia