IB/ipoib: Fix for use-after-free in ipoib_cm_tx_start

The following BUG was reported by kasan:

 BUG: KASAN: use-after-free in ipoib_cm_tx_start+0x430/0x1390 [ib_ipoib]
 Read of size 80 at addr ffff88034c30bcd0 by task kworker/u16:1/24020

 Workqueue: ipoib_wq ipoib_cm_tx_start [ib_ipoib]
 Call Trace:
  dump_stack+0x9a/0xeb
  print_address_description+0xe3/0x2e0
  kasan_report+0x18a/0x2e0
  ? ipoib_cm_tx_start+0x430/0x1390 [ib_ipoib]
  memcpy+0x1f/0x50
  ipoib_cm_tx_start+0x430/0x1390 [ib_ipoib]
  ? kvm_clock_read+0x1f/0x30
  ? ipoib_cm_skb_reap+0x610/0x610 [ib_ipoib]
  ? __lock_is_held+0xc2/0x170
  ? process_one_work+0x880/0x1960
  ? process_one_work+0x912/0x1960
  process_one_work+0x912/0x1960
  ? wq_pool_ids_show+0x310/0x310
  ? lock_acquire+0x145/0x440
  worker_thread+0x87/0xbb0
  ? process_one_work+0x1960/0x1960
  kthread+0x314/0x3d0
  ? kthread_create_worker_on_cpu+0xc0/0xc0
  ret_from_fork+0x3a/0x50

 Allocated by task 0:
  kasan_kmalloc+0xa0/0xd0
  kmem_cache_alloc_trace+0x168/0x3e0
  path_rec_create+0xa2/0x1f0 [ib_ipoib]
  ipoib_start_xmit+0xa98/0x19e0 [ib_ipoib]
  dev_hard_start_xmit+0x159/0x8d0
  sch_direct_xmit+0x226/0xb40
  __dev_queue_xmit+0x1d63/0x2950
  neigh_update+0x889/0x1770
  arp_process+0xc47/0x21f0
  arp_rcv+0x462/0x760
  __netif_receive_skb_core+0x1546/0x2da0
  netif_receive_skb_internal+0xf2/0x590
  napi_gro_receive+0x28e/0x390
  ipoib_ib_handle_rx_wc_rss+0x873/0x1b60 [ib_ipoib]
  ipoib_rx_poll_rss+0x17d/0x320 [ib_ipoib]
  net_rx_action+0x427/0xe30
  __do_softirq+0x28e/0xc42

 Freed by task 26680:
  __kasan_slab_free+0x11d/0x160
  kfree+0xf5/0x360
  ipoib_flush_paths+0x532/0x9d0 [ib_ipoib]
  ipoib_set_mode_rss+0x1ad/0x560 [ib_ipoib]
  set_mode+0xc8/0x150 [ib_ipoib]
  kernfs_fop_write+0x279/0x440
  __vfs_write+0xd8/0x5c0
  vfs_write+0x15e/0x470
  ksys_write+0xb8/0x180
  do_syscall_64+0x9b/0x420
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

 The buggy address belongs to the object at ffff88034c30bcc8
                which belongs to the cache kmalloc-512 of size 512
 The buggy address is located 8 bytes inside of
                512-byte region [ffff88034c30bcc8, ffff88034c30bec8)
 The buggy address belongs to the page:

The following race between change mode and xmit flow is the reason for
this use-after-free:

Change mode     Send packet 1 to GID XX      Send packet 2 to GID XX
     |                    |                             |
   start                  |                             |
     |                    |                             |
     |                    |                             |
     |         Create new path for GID XX               |
     |           and update neigh path                  |
     |                    |                             |
     |                    |                             |
     |                    |                             |
 flush_paths              |                             |
                          |                             |
               queue_work(cm.start_task)                |
                          |                 Path for GID XX not found
                          |                      create new path
                          |
                          |
               start_task runs with old
                    released path

There is no locking to protect the lifetime of the path through the
ipoib_cm_tx struct, so delete it entirely and always use the newly looked
up path under the priv->lock.

Fixes: 546481c2 ("IB/ipoib: Fix memory corruption in ipoib cm mode connect flow")
Signed-off-by: Feras Daoud <ferasda@mellanox.com>
Reviewed-by: Erez Shitrit <erezsh@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/ipoib/ipoib.h

@@ -248,7 +248,6 @@ struct ipoib_cm_tx {
 	struct list_head     list;
 	struct net_device   *dev;
 	struct ipoib_neigh  *neigh;
-	struct ipoib_path   *path;
 	struct ipoib_tx_buf *tx_ring;
 	unsigned int	     tx_head;
 	unsigned int	     tx_tail;

drivers/infiniband/ulp/ipoib/ipoib_cm.c

@@ -1312,7 +1312,6 @@ struct ipoib_cm_tx *ipoib_cm_create_tx(struct net_device *dev, struct ipoib_path
 
 	neigh->cm = tx;
 	tx->neigh = neigh;
-	tx->path = path;
 	tx->dev = dev;
 	list_add(&tx->list, &priv->cm.start_list);
 	set_bit(IPOIB_FLAG_INITIALIZED, &tx->flags);
@@ -1371,7 +1370,7 @@ static void ipoib_cm_tx_start(struct work_struct *work)
 				neigh->daddr + QPN_AND_OPTIONS_OFFSET);
 			goto free_neigh;
 		}
-		memcpy(&pathrec, &p->path->pathrec, sizeof(pathrec));
+		memcpy(&pathrec, &path->pathrec, sizeof(pathrec));
 
 		spin_unlock_irqrestore(&priv->lock, flags);
 		netif_tx_unlock_bh(dev);