netdevsim: Fix use-after-free during device dismantle

Commit da58f90f ("netdevsim: Add devlink-trap support") added
delayed work to netdevsim that periodically iterates over the registered
netdevsim ports and reports various packet traps via devlink.

While the delayed work takes the 'port_list_lock' mutex to protect
against concurrent addition / deletion of ports, during device creation
/ dismantle ports are added / deleted without this lock, which can
result in a use-after-free [1].

Fix this by making sure that the ports list is always modified under the
lock.

[1]
[   59.205543] ==================================================================
[   59.207748] BUG: KASAN: use-after-free in nsim_dev_trap_report_work+0xa67/0xad0
[   59.210247] Read of size 8 at addr ffff8883cbdd3398 by task kworker/3:1/38
[   59.212584]
[   59.213148] CPU: 3 PID: 38 Comm: kworker/3:1 Not tainted 5.4.0-rc3-custom-16119-ge6abb5f0261e #2013
[   59.215896] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20180724_192412-buildhw-07.phx2.fedoraproject.org-1.fc29 04/01/2014
[   59.218384] Workqueue: events nsim_dev_trap_report_work
[   59.219428] Call Trace:
[   59.219924]  dump_stack+0xa9/0x10e
[   59.220623]  print_address_description.constprop.4+0x21/0x340
[   59.221976]  ? vprintk_func+0x66/0x240
[   59.222752]  __kasan_report.cold.8+0x78/0x91
[   59.223602]  ? nsim_dev_trap_report_work+0xa67/0xad0
[   59.224603]  kasan_report+0xe/0x20
[   59.225296]  nsim_dev_trap_report_work+0xa67/0xad0
[   59.226435]  ? rcu_read_lock_sched_held+0xaf/0xe0
[   59.227512]  ? trace_event_raw_event_rcu_quiescent_state_report+0x360/0x360
[   59.228851]  process_one_work+0x98f/0x1760
[   59.229684]  ? pwq_dec_nr_in_flight+0x330/0x330
[   59.230656]  worker_thread+0x91/0xc40
[   59.231587]  ? process_one_work+0x1760/0x1760
[   59.232451]  kthread+0x34a/0x410
[   59.233104]  ? __kthread_queue_delayed_work+0x240/0x240
[   59.234141]  ret_from_fork+0x3a/0x50
[   59.234982]
[   59.235371] Allocated by task 187:
[   59.236189]  save_stack+0x19/0x80
[   59.236853]  __kasan_kmalloc.constprop.5+0xc1/0xd0
[   59.237822]  kmem_cache_alloc_trace+0x14c/0x380
[   59.238769]  __nsim_dev_port_add+0xaf/0x5c0
[   59.239627]  nsim_dev_probe+0x4fc/0x1140
[   59.240550]  really_probe+0x264/0xc00
[   59.241418]  driver_probe_device+0x208/0x2e0
[   59.242255]  __device_attach_driver+0x215/0x2d0
[   59.243150]  bus_for_each_drv+0x154/0x1d0
[   59.243944]  __device_attach+0x1ba/0x2b0
[   59.244923]  bus_probe_device+0x1dd/0x290
[   59.245805]  device_add+0xbac/0x1550
[   59.246528]  new_device_store+0x1f4/0x400
[   59.247306]  bus_attr_store+0x7b/0xa0
[   59.248047]  sysfs_kf_write+0x10f/0x170
[   59.248941]  kernfs_fop_write+0x283/0x430
[   59.249843]  __vfs_write+0x81/0x100
[   59.250546]  vfs_write+0x1ce/0x510
[   59.251190]  ksys_write+0x104/0x200
[   59.251873]  do_syscall_64+0xa4/0x4e0
[   59.252642]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   59.253837]
[   59.254203] Freed by task 187:
[   59.254811]  save_stack+0x19/0x80
[   59.255463]  __kasan_slab_free+0x125/0x170
[   59.256265]  kfree+0x100/0x440
[   59.256870]  nsim_dev_remove+0x98/0x100
[   59.257651]  nsim_bus_remove+0x16/0x20
[   59.258382]  device_release_driver_internal+0x20b/0x4d0
[   59.259588]  bus_remove_device+0x2e9/0x5a0
[   59.260551]  device_del+0x410/0xad0
[   59.263777]  device_unregister+0x26/0xc0
[   59.264616]  nsim_bus_dev_del+0x16/0x60
[   59.265381]  del_device_store+0x2d6/0x3c0
[   59.266295]  bus_attr_store+0x7b/0xa0
[   59.267192]  sysfs_kf_write+0x10f/0x170
[   59.267960]  kernfs_fop_write+0x283/0x430
[   59.268800]  __vfs_write+0x81/0x100
[   59.269551]  vfs_write+0x1ce/0x510
[   59.270252]  ksys_write+0x104/0x200
[   59.270910]  do_syscall_64+0xa4/0x4e0
[   59.271680]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   59.272812]
[   59.273211] The buggy address belongs to the object at ffff8883cbdd3200
[   59.273211]  which belongs to the cache kmalloc-512 of size 512
[   59.275838] The buggy address is located 408 bytes inside of
[   59.275838]  512-byte region [ffff8883cbdd3200, ffff8883cbdd3400)
[   59.278151] The buggy address belongs to the page:
[   59.279215] page:ffffea000f2f7400 refcount:1 mapcount:0 mapping:ffff8883ecc0ce00 index:0x0 compound_mapcount: 0
[   59.281449] flags: 0x200000000010200(slab|head)
[   59.282356] raw: 0200000000010200 ffffea000f2f3a08 ffffea000f2fd608 ffff8883ecc0ce00
[   59.283949] raw: 0000000000000000 0000000000150015 00000001ffffffff 0000000000000000
[   59.285608] page dumped because: kasan: bad access detected
[   59.286981]
[   59.287337] Memory state around the buggy address:
[   59.288310]  ffff8883cbdd3280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[   59.289763]  ffff8883cbdd3300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[   59.291452] >ffff8883cbdd3380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[   59.292945]                             ^
[   59.293815]  ffff8883cbdd3400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[   59.295220]  ffff8883cbdd3480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[   59.296872] ==================================================================

Fixes: da58f90f ("netdevsim: Add devlink-trap support")
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Reported-by: syzbot+9ed8f68ab30761f3678e@syzkaller.appspotmail.com
Acked-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/netdevsim/dev.c

@@ -806,9 +806,11 @@ static void nsim_dev_port_del_all(struct nsim_dev *nsim_dev)
 {
 	struct nsim_dev_port *nsim_dev_port, *tmp;
 
+	mutex_lock(&nsim_dev->port_list_lock);
 	list_for_each_entry_safe(nsim_dev_port, tmp,
 				 &nsim_dev->port_list, list)
 		__nsim_dev_port_del(nsim_dev_port);
+	mutex_unlock(&nsim_dev->port_list_lock);
 }
 
 int nsim_dev_probe(struct nsim_bus_dev *nsim_bus_dev)
@@ -822,14 +824,17 @@ int nsim_dev_probe(struct nsim_bus_dev *nsim_bus_dev)
 		return PTR_ERR(nsim_dev);
 	dev_set_drvdata(&nsim_bus_dev->dev, nsim_dev);
 
+	mutex_lock(&nsim_dev->port_list_lock);
 	for (i = 0; i < nsim_bus_dev->port_count; i++) {
 		err = __nsim_dev_port_add(nsim_dev, i);
 		if (err)
 			goto err_port_del_all;
 	}
+	mutex_unlock(&nsim_dev->port_list_lock);
 	return 0;
 
 err_port_del_all:
+	mutex_unlock(&nsim_dev->port_list_lock);
 	nsim_dev_port_del_all(nsim_dev);
 	nsim_dev_destroy(nsim_dev);
 	return err;