Re: [PATCH v3] IB/sa: Resolving use-after-free in ib_nl_send_msg

[Leon Romanovsky <leon@kernel.org>]

On Mon, Jun 08, 2020 at 07:46:16AM -0700, Divya Indi wrote:
> Commit 3ebd2fd0d011 ("IB/sa: Put netlink request into the request list before sending")'
> -
> 1. Adds the query to the request list before ib_nl_snd_msg.
> 2. Removes ib_nl_send_msg from within the spinlock which also makes it
> possible to allocate memory with GFP_KERNEL.
>
> 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 causing a use after free situation
> while accessing the query in ib_nl_send_msg.
>
> 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 the above issue -
> 1. Add the req to the request list only after the request has been sent out.
> 2. To handle the race where response comes in before adding request to
> the request list, send(rdma_nl_multicast) and add to list while holding the
> spinlock - request_lock.
> 3. Use GFP_NOWAIT for rdma_nl_multicast since it is called while holding
> a spinlock. In case of memory allocation failure, request will go out to SA.
>
> Signed-off-by: Divya Indi <divya.indi@oracle.com>
> Fixes: 3ebd2fd0d011 ("IB/sa: Put netlink request into the request list
> before sending")

Author SOB should be after "Fixes" line.

> ---
>  drivers/infiniband/core/sa_query.c | 34 +++++++++++++++++-----------------
>  1 file changed, 17 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/infiniband/core/sa_query.c b/drivers/infiniband/core/sa_query.c
> index 74e0058..042c99b 100644
> --- a/drivers/infiniband/core/sa_query.c
> +++ b/drivers/infiniband/core/sa_query.c
> @@ -836,6 +836,9 @@ static int ib_nl_send_msg(struct ib_sa_query *query, gfp_t gfp_mask)
>  	void *data;
>  	struct ib_sa_mad *mad;
>  	int len;
> +	unsigned long flags;
> +	unsigned long delay;
> +	int ret;
>
>  	mad = query->mad_buf->mad;
>  	len = ib_nl_get_path_rec_attrs_len(mad->sa_hdr.comp_mask);
> @@ -860,35 +863,32 @@ static int ib_nl_send_msg(struct ib_sa_query *query, gfp_t gfp_mask)
>  	/* Repair the nlmsg header length */
>  	nlmsg_end(skb, nlh);
>
> -	return rdma_nl_multicast(&init_net, skb, RDMA_NL_GROUP_LS, gfp_mask);
> +	spin_lock_irqsave(&ib_nl_request_lock, flags);
> +	ret =  rdma_nl_multicast(&init_net, skb, RDMA_NL_GROUP_LS, GFP_NOWAIT);

It is hard to be convinced that this is correct solution. The mix of
gfp_flags and GFP_NOWAIT at the same time and usage of
ib_nl_request_lock to protect lists and suddenly rdma_nl_multicast() too
makes this code unreadable/non-maintainable.

> +	if (!ret) {

Please use kernel coding style.

if (ret) {
  spin_unlock_irqrestore(&ib_nl_request_lock, flags);
  return ret;
  }

 ....

> +		/* Put the request on the list.*/
> +		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);
> +	}
> +	spin_unlock_irqrestore(&ib_nl_request_lock, flags);
> +
> +	return ret;
>  }
>
>  static int ib_nl_make_request(struct ib_sa_query *query, gfp_t gfp_mask)
>  {
> -	unsigned long flags;
> -	unsigned long delay;
>  	int ret;
>
>  	INIT_LIST_HEAD(&query->list);
>  	query->seq = (u32)atomic_inc_return(&ib_nl_sa_request_seq);
>
> -	/* Put the request on the list first.*/
> -	spin_lock_irqsave(&ib_nl_request_lock, flags);
> -	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);
> -	spin_unlock_irqrestore(&ib_nl_request_lock, flags);
> -
>  	ret = ib_nl_send_msg(query, gfp_mask);
>  	if (ret) {
>  		ret = -EIO;
> -		/* Remove the request */
> -		spin_lock_irqsave(&ib_nl_request_lock, flags);
> -		list_del(&query->list);
> -		spin_unlock_irqrestore(&ib_nl_request_lock, flags);
>  	}

Brackets should be removed too.
>
>  	return ret;
> --
> 1.8.3.1
>