RE: [PATCH 1/2] IB/sa: Resolving use-after-free in ib_nl_send_msg.

[Wan, Kaike]

> This patch fixes commit -
> commit 3ebd2fd0d011 ("IB/sa: Put netlink request into the request list
> before sending")'
> 
> Above commit adds the query to the request list before ib_nl_snd_msg.
> 
> However, if there is a delay in sending out the request (For
> eg: Delay due to low memory situation) the timer to handle request timeout
> might kick in before the request is sent out to ibacm via netlink.
> ib_nl_request_timeout may release the query if it fails to send it to SA as
> well causing a use after free situation.
> 
> Call Trace for the above race:
> 
> [<ffffffffa02f43cb>] ? ib_pack+0x17b/0x240 [ib_core] [<ffffffffa032aef1>]
> ib_sa_path_rec_get+0x181/0x200 [ib_sa] [<ffffffffa0379db0>]
> rdma_resolve_route+0x3c0/0x8d0 [rdma_cm] [<ffffffffa0374450>] ?
> cma_bind_port+0xa0/0xa0 [rdma_cm] [<ffffffffa040f850>] ?
> rds_rdma_cm_event_handler_cmn+0x850/0x850
> [rds_rdma]
> [<ffffffffa040f22c>] rds_rdma_cm_event_handler_cmn+0x22c/0x850
> [rds_rdma]
> [<ffffffffa040f860>] rds_rdma_cm_event_handler+0x10/0x20 [rds_rdma]
> [<ffffffffa037778e>] addr_handler+0x9e/0x140 [rdma_cm]
> [<ffffffffa026cdb4>] process_req+0x134/0x190 [ib_addr] [<ffffffff810a02f9>]
> process_one_work+0x169/0x4a0 [<ffffffff810a0b2b>]
> worker_thread+0x5b/0x560 [<ffffffff810a0ad0>] ?
> flush_delayed_work+0x50/0x50 [<ffffffff810a68fb>] kthread+0xcb/0xf0
> [<ffffffff816ec49a>] ? __schedule+0x24a/0x810 [<ffffffff816ec49a>] ?
> __schedule+0x24a/0x810 [<ffffffff810a6830>] ?
> kthread_create_on_node+0x180/0x180
> [<ffffffff816f25a7>] ret_from_fork+0x47/0x90 [<ffffffff810a6830>] ?
> kthread_create_on_node+0x180/0x180
> ....
> RIP  [<ffffffffa03296cd>] send_mad+0x33d/0x5d0 [ib_sa]
> 
> To resolve this issue, we introduce a new flag IB_SA_NL_QUERY_SENT.
> This flag Indicates if the request has been sent out to ibacm yet.
> 
> If this flag is not set for a query and the query times out, we add it back to
> the list with the original delay.
> 
> To handle the case where a response is received before we could set this flag,
> the response handler waits for the flag to be set before proceeding with the
> query.
> 
> Signed-off-by: Divya Indi <divya.indi@xxxxxxxxxx>
> ---
>  drivers/infiniband/core/sa_query.c | 45
> ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/drivers/infiniband/core/sa_query.c
> b/drivers/infiniband/core/sa_query.c
> index 30d4c12..ffbae2f 100644
> --- a/drivers/infiniband/core/sa_query.c
> +++ b/drivers/infiniband/core/sa_query.c
> @@ -59,6 +59,9 @@
>  #define IB_SA_LOCAL_SVC_TIMEOUT_MAX		200000
>  #define IB_SA_CPI_MAX_RETRY_CNT			3
>  #define IB_SA_CPI_RETRY_WAIT			1000 /*msecs */
> +
> +DECLARE_WAIT_QUEUE_HEAD(wait_queue);
> +
>  static int sa_local_svc_timeout_ms =
> IB_SA_LOCAL_SVC_TIMEOUT_DEFAULT;
> 
>  struct ib_sa_sm_ah {
> @@ -122,6 +125,7 @@ struct ib_sa_query {
>  #define IB_SA_ENABLE_LOCAL_SERVICE	0x00000001
>  #define IB_SA_CANCEL			0x00000002
>  #define IB_SA_QUERY_OPA			0x00000004
> +#define IB_SA_NL_QUERY_SENT		0x00000008
> 
>  struct ib_sa_service_query {
>  	void (*callback)(int, struct ib_sa_service_rec *, void *); @@ -746,6
> +750,11 @@ static inline int ib_sa_query_cancelled(struct ib_sa_query
> *query)
>  	return (query->flags & IB_SA_CANCEL);
>  }
> 
> +static inline int ib_sa_nl_query_sent(struct ib_sa_query *query) {
> +	return (query->flags & IB_SA_NL_QUERY_SENT); }
> +
>  static void ib_nl_set_path_rec_attrs(struct sk_buff *skb,
>  				     struct ib_sa_query *query)
>  {
> @@ -889,6 +898,15 @@ static int ib_nl_make_request(struct ib_sa_query
> *query, gfp_t gfp_mask)
>  		spin_lock_irqsave(&ib_nl_request_lock, flags);
>  		list_del(&query->list);
>  		spin_unlock_irqrestore(&ib_nl_request_lock, flags);
> +	} else {
> +		query->flags |= IB_SA_NL_QUERY_SENT;
> +
> +		/*
> +		 * If response is received before this flag was set
> +		 * someone is waiting to process the response and release
> the
> +		 * query.
> +		 */
> +		wake_up(&wait_queue);
>  	}
> 
>  	return ret;
> @@ -994,6 +1012,21 @@ static void ib_nl_request_timeout(struct
> work_struct *work)
>  		}
> 
>  		list_del(&query->list);
> +
> +		/*
> +		 * If IB_SA_NL_QUERY_SENT is not set, this query has not
> been
> +		 * sent to ibacm yet. Reset the timer.
> +		 */
> +		if (!ib_sa_nl_query_sent(query)) {
> +			delay = msecs_to_jiffies(sa_local_svc_timeout_ms);
> +			query->timeout = delay + jiffies;
> +			list_add_tail(&query->list, &ib_nl_request_list);
> +			/* Start the timeout if this is the only request */
> +			if (ib_nl_request_list.next == &query->list)
> +				queue_delayed_work(ib_nl_wq,
> &ib_nl_timed_work,
> +						delay);
> +			break;
> +		}
>  		ib_sa_disable_local_svc(query);
>  		/* Hold the lock to protect against query cancellation */
>  		if (ib_sa_query_cancelled(query))
> @@ -1123,6 +1156,18 @@ int ib_nl_handle_resolve_resp(struct sk_buff
> *skb,
> 
>  	send_buf = query->mad_buf;
> 
> +	/*
> +	 * Make sure the IB_SA_NL_QUERY_SENT flag is set before
> +	 * processing this query. If flag is not set, query can be accessed in
> +	 * another context while setting the flag and processing the query
> will
> +	 * eventually release it causing a possible use-after-free.
> +	 */
> +	if (unlikely(!ib_sa_nl_query_sent(query))) {
> +		spin_unlock_irqrestore(&ib_nl_request_lock, flags);
> +		wait_event(wait_queue, ib_sa_nl_query_sent(query));
> +		spin_lock_irqsave(&ib_nl_request_lock, flags);
> +	}
> +
>  	if (!ib_nl_is_good_resolve_resp(nlh)) {
>  		/* if the result is a failure, send out the packet via IB */
>  		ib_sa_disable_local_svc(query);
> --
> 1.8.3.1

Reviewd-by:  Kaike Wan <Kaike.wan@xxxxxxxxx>