RDMA/bnxt_re: Avoid accessing the device structure after it is freed

When bnxt_re_ib_reg returns failure, the device structure gets
freed. Driver tries to access the device pointer
after it is freed.

[ 4871.034744] Failed to register with netedev: 0xffffffa1
[ 4871.034765] infiniband (null): Failed to register with IB: 0xffffffea
[ 4871.046430] ==================================================================
[ 4871.046437] BUG: KASAN: use-after-free in bnxt_re_task+0x63/0x180 [bnxt_re]
[ 4871.046439] Write of size 4 at addr ffff880fa8406f48 by task kworker/u48:2/17813

[ 4871.046443] CPU: 20 PID: 17813 Comm: kworker/u48:2 Kdump: loaded Tainted: G B OE  4.20.0-rc1+ linux-sunxi#42
[ 4871.046444] Hardware name: Dell Inc. PowerEdge R730/0599V5, BIOS 1.0.4 08/28/2014
[ 4871.046447] Workqueue: bnxt_re bnxt_re_task [bnxt_re]
[ 4871.046449] Call Trace:
[ 4871.046454]  dump_stack+0x91/0xeb
[ 4871.046458]  print_address_description+0x6a/0x2a0
[ 4871.046461]  kasan_report+0x176/0x2d0
[ 4871.046463]  ? bnxt_re_task+0x63/0x180 [bnxt_re]
[ 4871.046466]  bnxt_re_task+0x63/0x180 [bnxt_re]
[ 4871.046470]  process_one_work+0x216/0x5b0
[ 4871.046471]  ? process_one_work+0x189/0x5b0
[ 4871.046475]  worker_thread+0x4e/0x3d0
[ 4871.046479]  kthread+0x10e/0x140
[ 4871.046480]  ? process_one_work+0x5b0/0x5b0
[ 4871.046482]  ? kthread_stop+0x220/0x220
[ 4871.046486]  ret_from_fork+0x3a/0x50

[ 4871.046492] The buggy address belongs to the page:
[ 4871.046494] page:ffffea003ea10180 count:0 mapcount:0 mapping:0000000000000000 index:0x0
[ 4871.046495] flags: 0x57ffffc0000000()
[ 4871.046498] raw: 0057ffffc0000000 0000000000000000 ffffea003ea10188 0000000000000000
[ 4871.046500] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[ 4871.046501] page dumped because: kasan: bad access detected

Avoid accessing the device structure once it is freed.

Fixes: 497158a ("RDMA/bnxt_re: Fix the ib_reg failure cleanup")
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/bnxt_re/main.c

@@ -1467,6 +1467,7 @@ static void bnxt_re_task(struct work_struct *work)
 				"Failed to register with IB: %#x", rc);
 			bnxt_re_remove_one(rdev);
 			bnxt_re_dev_unreg(rdev);
+			goto exit;
 		}
 		break;
 	case NETDEV_UP:
@@ -1490,6 +1491,7 @@ static void bnxt_re_task(struct work_struct *work)
 	}
 	smp_mb__before_atomic();
 	atomic_dec(&rdev->sched_count);
+exit:
 	kfree(re_work);
 }