Review Request

Review Request

[Divya Indi]

[PATCH v2] IB/sa: Resolving use-after-free in ib_nl_send_msg.

Hi,

This is the v2 of the patch that addresses the comments received for v1 -

- Using atomic bit ops for setting and testing IB_SA_NL_QUERY_SENT.
- Rewording and adding comments.


Thanks,
Divya

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

[Divya Indi]

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@oracle.com>
---
 drivers/infiniband/core/sa_query.c | 53 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/infiniband/core/sa_query.c b/drivers/infiniband/core/sa_query.c
index 30d4c12..91486e7 100644
--- a/drivers/infiniband/core/sa_query.c
+++ b/drivers/infiniband/core/sa_query.c
@@ -42,6 +42,7 @@
 #include <linux/kref.h>
 #include <linux/xarray.h>
 #include <linux/workqueue.h>
+#include <linux/bitops.h>
 #include <uapi/linux/if_ether.h>
 #include <rdma/ib_pack.h>
 #include <rdma/ib_cache.h>
@@ -59,6 +60,9 @@
 #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 {
@@ -123,6 +127,12 @@ struct ib_sa_query {
 #define IB_SA_CANCEL			0x00000002
 #define IB_SA_QUERY_OPA			0x00000004
 
+/*
+ * This bit in the SA query flags indicates whether the query
+ * has been sent out to ibacm via netlink
+ */
+#define IB_SA_NL_QUERY_SENT		3
+
 struct ib_sa_service_query {
 	void (*callback)(int, struct ib_sa_service_rec *, void *);
 	void *context;
@@ -746,6 +756,11 @@ 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 test_bit(IB_SA_NL_QUERY_SENT, (unsigned long *)&query->flags);
+}
+
 static void ib_nl_set_path_rec_attrs(struct sk_buff *skb,
 				     struct ib_sa_query *query)
 {
@@ -889,6 +904,15 @@ 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 {
+		set_bit(IB_SA_NL_QUERY_SENT, (unsigned long *)&query->flags);
+
+		/*
+		 * 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 +1018,21 @@ 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))
@@ -1122,6 +1161,20 @@ int ib_nl_handle_resolve_resp(struct sk_buff *skb,
 	}
 
 	send_buf = query->mad_buf;
+	/*
+	 * In case of a quick response ie when a response comes in before
+	 * setting IB_SA_NL_QUERY_SENT, we can have an unlikely race where the
+	 * response handler will release the query, but we can still access the
+	 * freed query while setting the flag.
+	 * Hence, before proceeding and eventually releasing the query -
+	 * wait till the flag is set. The flag should be set soon since getting
+	 * a response is indicative of having successfully sent the query.
+	 */
+	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 */
-- 
1.8.3.1

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

[Jason Gunthorpe]

On Thu, May 14, 2020 at 08:11:24AM -0700, Divya Indi wrote:
>  static void ib_nl_set_path_rec_attrs(struct sk_buff *skb,
>  				     struct ib_sa_query *query)
>  {
> @@ -889,6 +904,15 @@ 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 {
> +		set_bit(IB_SA_NL_QUERY_SENT, (unsigned long *)&query->flags);
> +
> +		/*
> +		 * If response is received before this flag was set
> +		 * someone is waiting to process the response and release the
> +		 * query.
> +		 */
> +		wake_up(&wait_queue);
>  	}

As far as I can see the issue here is that the request is put into the
ib_nl_request_list before it is really ready to be in that list, eg
ib_nl_send_msg() has actually completed and ownership of the memory
has been transfered.

It appears to me the reason for this is simply because a spinlock is
used for the ib_nl_request_lock and it cannot be held across
ib_nl_send_msg().

Convert that lock to a mutex and move the list_add to after the
success of ib_nl_send_msg() and this bug should be fixed without
adding jaunty atomics or a wait queue.

This is a 'racy error unwind' bug class...

Jason