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

[Divya Indi]

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@xxxxxxxxxx>
Fixes: 3ebd2fd0d011 ("IB/sa: Put netlink request into the request list
before sending")
---
 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);
+	if (!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);
 	}
 
 	return ret;
-- 
1.8.3.1