net/mlx5e: Lag, Fix use-after-free in fib event handler

Recent commit that modified fib route event handler to handle events
according to their priority introduced use-after-free[0] in mp->mfi pointer
usage. The pointer now is not just cached in order to be compared to
following fib_info instances, but is also dereferenced to obtain
fib_priority. However, since mlx5 lag code doesn't hold the reference to
fin_info during whole mp->mfi lifetime, it could be used after fib_info
instance has already been freed be kernel infrastructure code.

Don't ever dereference mp->mfi pointer. Refactor it to be 'const void*'
type and cache fib_info priority in dedicated integer. Group
fib_info-related data into dedicated 'fib' structure that will be further
extended by following patches in the series.

[0]:

[  203.588029] ==================================================================
[  203.590161] BUG: KASAN: use-after-free in mlx5_lag_fib_update+0xabd/0xd60 [mlx5_core]
[  203.592386] Read of size 4 at addr ffff888144df2050 by task kworker/u20:4/138

[  203.594766] CPU: 3 PID: 138 Comm: kworker/u20:4 Tainted: G    B             5.17.0-rc7+ #6
[  203.596751] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[  203.598813] Workqueue: mlx5_lag_mp mlx5_lag_fib_update [mlx5_core]
[  203.600053] Call Trace:
[  203.600608]  <TASK>
[  203.601110]  dump_stack_lvl+0x48/0x5e
[  203.601860]  print_address_description.constprop.0+0x1f/0x160
[  203.602950]  ? mlx5_lag_fib_update+0xabd/0xd60 [mlx5_core]
[  203.604073]  ? mlx5_lag_fib_update+0xabd/0xd60 [mlx5_core]
[  203.605177]  kasan_report.cold+0x83/0xdf
[  203.605969]  ? mlx5_lag_fib_update+0xabd/0xd60 [mlx5_core]
[  203.607102]  mlx5_lag_fib_update+0xabd/0xd60 [mlx5_core]
[  203.608199]  ? mlx5_lag_init_fib_work+0x1c0/0x1c0 [mlx5_core]
[  203.609382]  ? read_word_at_a_time+0xe/0x20
[  203.610463]  ? strscpy+0xa0/0x2a0
[  203.611463]  process_one_work+0x722/0x1270
[  203.612344]  worker_thread+0x540/0x11e0
[  203.613136]  ? rescuer_thread+0xd50/0xd50
[  203.613949]  kthread+0x26e/0x300
[  203.614627]  ? kthread_complete_and_exit+0x20/0x20
[  203.615542]  ret_from_fork+0x1f/0x30
[  203.616273]  </TASK>

[  203.617174] Allocated by task 3746:
[  203.617874]  kasan_save_stack+0x1e/0x40
[  203.618644]  __kasan_kmalloc+0x81/0xa0
[  203.619394]  fib_create_info+0xb41/0x3c50
[  203.620213]  fib_table_insert+0x190/0x1ff0
[  203.621020]  fib_magic.isra.0+0x246/0x2e0
[  203.621803]  fib_add_ifaddr+0x19f/0x670
[  203.622563]  fib_inetaddr_event+0x13f/0x270
[  203.623377]  blocking_notifier_call_chain+0xd4/0x130
[  203.624355]  __inet_insert_ifa+0x641/0xb20
[  203.625185]  inet_rtm_newaddr+0xc3d/0x16a0
[  203.626009]  rtnetlink_rcv_msg+0x309/0x880
[  203.626826]  netlink_rcv_skb+0x11d/0x340
[  203.627626]  netlink_unicast+0x4cc/0x790
[  203.628430]  netlink_sendmsg+0x762/0xc00
[  203.629230]  sock_sendmsg+0xb2/0xe0
[  203.629955]  ____sys_sendmsg+0x58a/0x770
[  203.630756]  ___sys_sendmsg+0xd8/0x160
[  203.631523]  __sys_sendmsg+0xb7/0x140
[  203.632294]  do_syscall_64+0x35/0x80
[  203.633045]  entry_SYSCALL_64_after_hwframe+0x44/0xae

[  203.634427] Freed by task 0:
[  203.635063]  kasan_save_stack+0x1e/0x40
[  203.635844]  kasan_set_track+0x21/0x30
[  203.636618]  kasan_set_free_info+0x20/0x30
[  203.637450]  __kasan_slab_free+0xfc/0x140
[  203.638271]  kfree+0x94/0x3b0
[  203.638903]  rcu_core+0x5e4/0x1990
[  203.639640]  __do_softirq+0x1ba/0x5d3

[  203.640828] Last potentially related work creation:
[  203.641785]  kasan_save_stack+0x1e/0x40
[  203.642571]  __kasan_record_aux_stack+0x9f/0xb0
[  203.643478]  call_rcu+0x88/0x9c0
[  203.644178]  fib_release_info+0x539/0x750
[  203.644997]  fib_table_delete+0x659/0xb80
[  203.645809]  fib_magic.isra.0+0x1a3/0x2e0
[  203.646617]  fib_del_ifaddr+0x93f/0x1300
[  203.647415]  fib_inetaddr_event+0x9f/0x270
[  203.648251]  blocking_notifier_call_chain+0xd4/0x130
[  203.649225]  __inet_del_ifa+0x474/0xc10
[  203.650016]  devinet_ioctl+0x781/0x17f0
[  203.650788]  inet_ioctl+0x1ad/0x290
[  203.651533]  sock_do_ioctl+0xce/0x1c0
[  203.652315]  sock_ioctl+0x27b/0x4f0
[  203.653058]  __x64_sys_ioctl+0x124/0x190
[  203.653850]  do_syscall_64+0x35/0x80
[  203.654608]  entry_SYSCALL_64_after_hwframe+0x44/0xae

[  203.666952] The buggy address belongs to the object at ffff888144df2000
                which belongs to the cache kmalloc-256 of size 256
[  203.669250] The buggy address is located 80 bytes inside of
                256-byte region [ffff888144df2000, ffff888144df2100)
[  203.671332] The buggy address belongs to the page:
[  203.672273] page:00000000bf6c9314 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x144df0
[  203.674009] head:00000000bf6c9314 order:2 compound_mapcount:0 compound_pincount:0
[  203.675422] flags: 0x2ffff800010200(slab|head|node=0|zone=2|lastcpupid=0x1ffff)
[  203.676819] raw: 002ffff800010200 0000000000000000 dead000000000122 ffff888100042b40
[  203.678384] raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
[  203.679928] page dumped because: kasan: bad access detected

[  203.681455] Memory state around the buggy address:
[  203.682421]  ffff888144df1f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  203.683863]  ffff888144df1f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  203.685310] >ffff888144df2000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  203.686701]                                                  ^
[  203.687820]  ffff888144df2080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  203.689226]  ffff888144df2100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  203.690620] ==================================================================

Fixes: ad11c4f1 ("net/mlx5e: Lag, Only handle events from highest priority multipath entry")
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/lag/mp.c

@@ -100,6 +100,12 @@ static void mlx5_lag_fib_event_flush(struct notifier_block *nb)
 	flush_workqueue(mp->wq);
 }
 
+static void mlx5_lag_fib_set(struct lag_mp *mp, struct fib_info *fi)
+{
+	mp->fib.mfi = fi;
+	mp->fib.priority = fi->fib_priority;
+}
+
 struct mlx5_fib_event_work {
 	struct work_struct work;
 	struct mlx5_lag *ldev;
@@ -121,13 +127,13 @@ static void mlx5_lag_fib_route_event(struct mlx5_lag *ldev,
 	/* Handle delete event */
 	if (event == FIB_EVENT_ENTRY_DEL) {
 		/* stop track */
-		if (mp->mfi == fi)
-			mp->mfi = NULL;
+		if (mp->fib.mfi == fi)
+			mp->fib.mfi = NULL;
 		return;
 	}
 
 	/* Handle multipath entry with lower priority value */
-	if (mp->mfi && mp->mfi != fi && fi->fib_priority >= mp->mfi->fib_priority)
+	if (mp->fib.mfi && mp->fib.mfi != fi && fi->fib_priority >= mp->fib.priority)
 		return;
 
 	/* Handle add/replace event */
@@ -145,7 +151,7 @@ static void mlx5_lag_fib_route_event(struct mlx5_lag *ldev,
 			mlx5_lag_set_port_affinity(ldev, i);
 		}
 
-		mp->mfi = fi;
+		mlx5_lag_fib_set(mp, fi);
 		return;
 	}
 
@@ -165,7 +171,7 @@ static void mlx5_lag_fib_route_event(struct mlx5_lag *ldev,
 	}
 
 	/* First time we see multipath route */
-	if (!mp->mfi && !__mlx5_lag_is_active(ldev)) {
+	if (!mp->fib.mfi && !__mlx5_lag_is_active(ldev)) {
 		struct lag_tracker tracker;
 
 		tracker = ldev->tracker;
@@ -173,7 +179,7 @@ static void mlx5_lag_fib_route_event(struct mlx5_lag *ldev,
 	}
 
 	mlx5_lag_set_port_affinity(ldev, MLX5_LAG_NORMAL_AFFINITY);
-	mp->mfi = fi;
+	mlx5_lag_fib_set(mp, fi);
 }
 
 static void mlx5_lag_fib_nexthop_event(struct mlx5_lag *ldev,
@@ -184,7 +190,7 @@ static void mlx5_lag_fib_nexthop_event(struct mlx5_lag *ldev,
 	struct lag_mp *mp = &ldev->lag_mp;
 
 	/* Check the nh event is related to the route */
-	if (!mp->mfi || mp->mfi != fi)
+	if (!mp->fib.mfi || mp->fib.mfi != fi)
 		return;
 
 	/* nh added/removed */
@@ -313,7 +319,7 @@ void mlx5_lag_mp_reset(struct mlx5_lag *ldev)
 	/* Clear mfi, as it might become stale when a route delete event
 	 * has been missed, see mlx5_lag_fib_route_event().
 	 */
-	ldev->lag_mp.mfi = NULL;
+	ldev->lag_mp.fib.mfi = NULL;
 }
 
 int mlx5_lag_mp_init(struct mlx5_lag *ldev)
@@ -324,7 +330,7 @@ int mlx5_lag_mp_init(struct mlx5_lag *ldev)
 	/* always clear mfi, as it might become stale when a route delete event
 	 * has been missed
 	 */
-	mp->mfi = NULL;
+	mp->fib.mfi = NULL;
 
 	if (mp->fib_nb.notifier_call)
 		return 0;
@@ -354,5 +360,5 @@ void mlx5_lag_mp_cleanup(struct mlx5_lag *ldev)
 	unregister_fib_notifier(&init_net, &mp->fib_nb);
 	destroy_workqueue(mp->wq);
 	mp->fib_nb.notifier_call = NULL;
-	mp->mfi = NULL;
+	mp->fib.mfi = NULL;
 }

drivers/net/ethernet/mellanox/mlx5/core/lag/mp.h

@@ -15,7 +15,10 @@ enum mlx5_lag_port_affinity {
 
 struct lag_mp {
 	struct notifier_block     fib_nb;
-	struct fib_info           *mfi; /* used in tracking fib events */
+	struct {
+		const void        *mfi; /* used in tracking fib events */
+		u32               priority;
+	} fib;
 	struct workqueue_struct   *wq;
 };