Re: [PATCH net v2 2/2] net/smc: fix LGR and link use-after-free issue

[Wenjia Zhang <wenjia@linux.ibm.com>]

On 27.11.24 14:30, 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.
> 
>   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() from
> server listening path are not protected by sock lock.
> 
> e.g.
> 
> Calls under socklock        | smc_listen_work
> -------------------------------------------------------
> lock_sock(sk)               | smc_conn_abort
> smc_conn_free               | \- smc_conn_free
> \- smcr_link_put            |    \- smcr_link_put (duplicated)
> release_sock(sk)
> 
> So here add sock lock protection in smc_listen_work() path, making it
> exclusive with other connection operations.
> 
> Fixes: 3b2dec2603d5 ("net/smc: restructure client and server code in af_smc")
> 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 | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index ed6d4d520bc7..9e6c69d18581 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -1900,6 +1900,7 @@ static void smc_listen_out(struct smc_sock *new_smc)
>   	if (tcp_sk(new_smc->clcsock->sk)->syn_smc)
>   		atomic_dec(&lsmc->queued_smc_hs);
>   
> +	release_sock(newsmcsk); /* lock in smc_listen_work() */
>   	if (lsmc->sk.sk_state == SMC_LISTEN) {
>   		lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING);
>   		smc_accept_enqueue(&lsmc->sk, newsmcsk);
> @@ -2421,6 +2422,7 @@ static void smc_listen_work(struct work_struct *work)
>   	u8 accept_version;
>   	int rc = 0;
>   
> +	lock_sock(&new_smc->sk); /* release in smc_listen_out() */
>   	if (new_smc->listen_smc->sk.sk_state != SMC_LISTEN)
>   		return smc_listen_out_err(new_smc);
>   

It looked much clearer than the last version to me! Thank you for fixing it!

Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>

Thanks,
Wenjia