[PATCH net 0/3] mlxsw: Three (m)router fixes

[PATCH net 0/3] mlxsw: Three (m)router fixes

[Petr Machata]

This patchset contains two fixes in mlxsw Spectrum router code, and one for
the Spectrum multicast router code. Please see the individual patches for
more details.

Ido Schimmel (3):
  mlxsw: spectrum_router: Fix possible neighbour reference count leak
  mlxsw: spectrum_router: Fix neighbour use-after-free
  mlxsw: spectrum_mr: Fix use-after-free when updating multicast route
    stats

 .../net/ethernet/mellanox/mlxsw/spectrum_mr.c |  2 ++
 .../ethernet/mellanox/mlxsw/spectrum_router.c | 27 ++++++++++---------
 2 files changed, 16 insertions(+), 13 deletions(-)

-- 
2.51.1

[PATCH net 1/3] mlxsw: spectrum_router: Fix possible neighbour reference count leak

[Petr Machata]

From: Ido Schimmel <idosch@nvidia.com>

mlxsw_sp_router_schedule_work() takes a reference on a neighbour,
expecting a work item to release it later on. However, we might fail to
schedule the work item, in which case the neighbour reference count will
be leaked.

Fix by taking the reference just before scheduling the work item. Note
that mlxsw_sp_router_schedule_work() can receive a NULL neighbour
pointer, but neigh_clone() handles that correctly.

Spotted during code review, did not actually observe the reference count
leak.

Fixes: 151b89f6025a ("mlxsw: spectrum_router: Reuse work neighbor initialization in work scheduler")
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
---

CC: Simon Horman <horms@kernel.org>

---
 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
index a2033837182e..f4e9ecaeb104 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
@@ -2858,6 +2858,11 @@ static int mlxsw_sp_router_schedule_work(struct net *net,
 	if (!net_work)
 		return NOTIFY_BAD;
 
+	/* Take a reference to ensure the neighbour won't be destructed until
+	 * we drop the reference in the work item.
+	 */
+	neigh_clone(n);
+
 	INIT_WORK(&net_work->work, cb);
 	net_work->mlxsw_sp = router->mlxsw_sp;
 	net_work->n = n;
@@ -2881,11 +2886,6 @@ static int mlxsw_sp_router_schedule_neigh_work(struct mlxsw_sp_router *router,
 	struct net *net;
 
 	net = neigh_parms_net(n->parms);
-
-	/* Take a reference to ensure the neighbour won't be destructed until we
-	 * drop the reference in delayed work.
-	 */
-	neigh_clone(n);
 	return mlxsw_sp_router_schedule_work(net, router, n,
 					     mlxsw_sp_router_neigh_event_work);
 }
-- 
2.51.1

Re: [PATCH net 1/3] mlxsw: spectrum_router: Fix possible neighbour reference count leak

[Simon Horman]

On Tue, Dec 02, 2025 at 06:44:11PM +0100, Petr Machata wrote:
> From: Ido Schimmel <idosch@nvidia.com>
> 
> mlxsw_sp_router_schedule_work() takes a reference on a neighbour,
> expecting a work item to release it later on. However, we might fail to
> schedule the work item, in which case the neighbour reference count will
> be leaked.
> 
> Fix by taking the reference just before scheduling the work item. Note
> that mlxsw_sp_router_schedule_work() can receive a NULL neighbour
> pointer, but neigh_clone() handles that correctly.
> 
> Spotted during code review, did not actually observe the reference count
> leak.
> 
> Fixes: 151b89f6025a ("mlxsw: spectrum_router: Reuse work neighbor initialization in work scheduler")
> Reviewed-by: Petr Machata <petrm@nvidia.com>
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
> Signed-off-by: Petr Machata <petrm@nvidia.com>

Reviewed-by: Simon Horman <horms@kernel.org>

[PATCH net 2/3] mlxsw: spectrum_router: Fix neighbour use-after-free

[Petr Machata]

From: Ido Schimmel <idosch@nvidia.com>

We sometimes observe use-after-free when dereferencing a neighbour [1].
The problem seems to be that the driver stores a pointer to the
neighbour, but without holding a reference on it. A reference is only
taken when the neighbour is used by a nexthop.

Fix by simplifying the reference counting scheme. Always take a
reference when storing a neighbour pointer in a neighbour entry. Avoid
taking a referencing when the neighbour is used by a nexthop as the
neighbour entry associated with the nexthop already holds a reference.

Tested by running the test that uncovered the problem over 300 times.
Without this patch the problem was reproduced after a handful of
iterations.

[1]
BUG: KASAN: slab-use-after-free in mlxsw_sp_neigh_entry_update+0x2d4/0x310
Read of size 8 at addr ffff88817f8e3420 by task ip/3929

CPU: 3 UID: 0 PID: 3929 Comm: ip Not tainted 6.18.0-rc4-virtme-g36b21a067510 #3 PREEMPT(full)
Hardware name: Nvidia SN5600/VMOD0013, BIOS 5.13 05/31/2023
Call Trace:
 <TASK>
 dump_stack_lvl+0x6f/0xa0
 print_address_description.constprop.0+0x6e/0x300
 print_report+0xfc/0x1fb
 kasan_report+0xe4/0x110
 mlxsw_sp_neigh_entry_update+0x2d4/0x310
 mlxsw_sp_router_rif_gone_sync+0x35f/0x510
 mlxsw_sp_rif_destroy+0x1ea/0x730
 mlxsw_sp_inetaddr_port_vlan_event+0xa1/0x1b0
 __mlxsw_sp_inetaddr_lag_event+0xcc/0x130
 __mlxsw_sp_inetaddr_event+0xf5/0x3c0
 mlxsw_sp_router_netdevice_event+0x1015/0x1580
 notifier_call_chain+0xcc/0x150
 call_netdevice_notifiers_info+0x7e/0x100
 __netdev_upper_dev_unlink+0x10b/0x210
 netdev_upper_dev_unlink+0x79/0xa0
 vrf_del_slave+0x18/0x50
 do_set_master+0x146/0x7d0
 do_setlink.isra.0+0x9a0/0x2880
 rtnl_newlink+0x637/0xb20
 rtnetlink_rcv_msg+0x6fe/0xb90
 netlink_rcv_skb+0x123/0x380
 netlink_unicast+0x4a3/0x770
 netlink_sendmsg+0x75b/0xc90
 __sock_sendmsg+0xbe/0x160
 ____sys_sendmsg+0x5b2/0x7d0
 ___sys_sendmsg+0xfd/0x180
 __sys_sendmsg+0x124/0x1c0
 do_syscall_64+0xbb/0xfd0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53
[...]

Allocated by task 109:
 kasan_save_stack+0x30/0x50
 kasan_save_track+0x14/0x30
 __kasan_kmalloc+0x7b/0x90
 __kmalloc_noprof+0x2c1/0x790
 neigh_alloc+0x6af/0x8f0
 ___neigh_create+0x63/0xe90
 mlxsw_sp_nexthop_neigh_init+0x430/0x7e0
 mlxsw_sp_nexthop_type_init+0x212/0x960
 mlxsw_sp_nexthop6_group_info_init.constprop.0+0x81f/0x1280
 mlxsw_sp_nexthop6_group_get+0x392/0x6a0
 mlxsw_sp_fib6_entry_create+0x46a/0xfd0
 mlxsw_sp_router_fib6_replace+0x1ed/0x5f0
 mlxsw_sp_router_fib6_event_work+0x10a/0x2a0
 process_one_work+0xd57/0x1390
 worker_thread+0x4d6/0xd40
 kthread+0x355/0x5b0
 ret_from_fork+0x1d4/0x270
 ret_from_fork_asm+0x11/0x20

Freed by task 154:
 kasan_save_stack+0x30/0x50
 kasan_save_track+0x14/0x30
 __kasan_save_free_info+0x3b/0x60
 __kasan_slab_free+0x43/0x70
 kmem_cache_free_bulk.part.0+0x1eb/0x5e0
 kvfree_rcu_bulk+0x1f2/0x260
 kfree_rcu_work+0x130/0x1b0
 process_one_work+0xd57/0x1390
 worker_thread+0x4d6/0xd40
 kthread+0x355/0x5b0
 ret_from_fork+0x1d4/0x270
 ret_from_fork_asm+0x11/0x20

Last potentially related work creation:
 kasan_save_stack+0x30/0x50
 kasan_record_aux_stack+0x8c/0xa0
 kvfree_call_rcu+0x93/0x5b0
 mlxsw_sp_router_neigh_event_work+0x67d/0x860
 process_one_work+0xd57/0x1390
 worker_thread+0x4d6/0xd40
 kthread+0x355/0x5b0
 ret_from_fork+0x1d4/0x270
 ret_from_fork_asm+0x11/0x20

Fixes: 6cf3c971dc84 ("mlxsw: spectrum_router: Add private neigh table")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
---

CC: Jiri Pirko <jiri@resnulli.us>

---
 .../ethernet/mellanox/mlxsw/spectrum_router.c   | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
index f4e9ecaeb104..2d0e89bd2fb9 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
@@ -2265,6 +2265,7 @@ mlxsw_sp_neigh_entry_alloc(struct mlxsw_sp *mlxsw_sp, struct neighbour *n,
 	if (!neigh_entry)
 		return NULL;
 
+	neigh_hold(n);
 	neigh_entry->key.n = n;
 	neigh_entry->rif = rif;
 	INIT_LIST_HEAD(&neigh_entry->nexthop_list);
@@ -2274,6 +2275,7 @@ mlxsw_sp_neigh_entry_alloc(struct mlxsw_sp *mlxsw_sp, struct neighbour *n,
 
 static void mlxsw_sp_neigh_entry_free(struct mlxsw_sp_neigh_entry *neigh_entry)
 {
+	neigh_release(neigh_entry->key.n);
 	kfree(neigh_entry);
 }
 
@@ -4320,6 +4322,8 @@ mlxsw_sp_nexthop_dead_neigh_replace(struct mlxsw_sp *mlxsw_sp,
 	if (err)
 		goto err_neigh_entry_insert;
 
+	neigh_release(old_n);
+
 	read_lock_bh(&n->lock);
 	nud_state = n->nud_state;
 	dead = n->dead;
@@ -4328,14 +4332,10 @@ mlxsw_sp_nexthop_dead_neigh_replace(struct mlxsw_sp *mlxsw_sp,
 
 	list_for_each_entry(nh, &neigh_entry->nexthop_list,
 			    neigh_list_node) {
-		neigh_release(old_n);
-		neigh_clone(n);
 		__mlxsw_sp_nexthop_neigh_update(nh, !entry_connected);
 		mlxsw_sp_nexthop_group_refresh(mlxsw_sp, nh->nhgi->nh_grp);
 	}
 
-	neigh_release(n);
-
 	return 0;
 
 err_neigh_entry_insert:
@@ -4428,6 +4428,11 @@ static int mlxsw_sp_nexthop_neigh_init(struct mlxsw_sp *mlxsw_sp,
 		}
 	}
 
+	/* Release the reference taken by neigh_lookup() / neigh_create() since
+	 * neigh_entry already holds one.
+	 */
+	neigh_release(n);
+
 	/* If that is the first nexthop connected to that neigh, add to
 	 * nexthop_neighs_list
 	 */
@@ -4454,11 +4459,9 @@ static void mlxsw_sp_nexthop_neigh_fini(struct mlxsw_sp *mlxsw_sp,
 					struct mlxsw_sp_nexthop *nh)
 {
 	struct mlxsw_sp_neigh_entry *neigh_entry = nh->neigh_entry;
-	struct neighbour *n;
 
 	if (!neigh_entry)
 		return;
-	n = neigh_entry->key.n;
 
 	__mlxsw_sp_nexthop_neigh_update(nh, true);
 	list_del(&nh->neigh_list_node);
@@ -4472,8 +4475,6 @@ static void mlxsw_sp_nexthop_neigh_fini(struct mlxsw_sp *mlxsw_sp,
 
 	if (!neigh_entry->connected && list_empty(&neigh_entry->nexthop_list))
 		mlxsw_sp_neigh_entry_destroy(mlxsw_sp, neigh_entry);
-
-	neigh_release(n);
 }
 
 static bool mlxsw_sp_ipip_netdev_ul_up(struct net_device *ol_dev)
-- 
2.51.1

Re: [PATCH net 2/3] mlxsw: spectrum_router: Fix neighbour use-after-free

[Simon Horman]

On Tue, Dec 02, 2025 at 06:44:12PM +0100, Petr Machata wrote:
> From: Ido Schimmel <idosch@nvidia.com>
> 
> We sometimes observe use-after-free when dereferencing a neighbour [1].
> The problem seems to be that the driver stores a pointer to the
> neighbour, but without holding a reference on it. A reference is only
> taken when the neighbour is used by a nexthop.
> 
> Fix by simplifying the reference counting scheme. Always take a
> reference when storing a neighbour pointer in a neighbour entry. Avoid
> taking a referencing when the neighbour is used by a nexthop as the
> neighbour entry associated with the nexthop already holds a reference.
> 
> Tested by running the test that uncovered the problem over 300 times.
> Without this patch the problem was reproduced after a handful of
> iterations.

...

> Fixes: 6cf3c971dc84 ("mlxsw: spectrum_router: Add private neigh table")
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
> Reviewed-by: Petr Machata <petrm@nvidia.com>
> Signed-off-by: Petr Machata <petrm@nvidia.com>


Reviewed-by: Simon Horman <horms@kernel.org>


...

[PATCH net 3/3] mlxsw: spectrum_mr: Fix use-after-free when updating multicast route stats

[Petr Machata]

From: Ido Schimmel <idosch@nvidia.com>

Cited commit added a dedicated mutex (instead of RTNL) to protect the
multicast route list, so that it will not change while the driver
periodically traverses it in order to update the kernel about multicast
route stats that were queried from the device.

One instance of list entry deletion (during route replace) was missed
and it can result in a use-after-free [1].

Fix by acquiring the mutex before deleting the entry from the list and
releasing it afterwards.

[1]
BUG: KASAN: slab-use-after-free in mlxsw_sp_mr_stats_update+0x4a5/0x540 drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c:1006 [mlxsw_spectrum]
Read of size 8 at addr ffff8881523c2fa8 by task kworker/2:5/22043

CPU: 2 UID: 0 PID: 22043 Comm: kworker/2:5 Not tainted 6.18.0-rc1-custom-g1a3d6d7cd014 #1 PREEMPT(full)
Hardware name: Mellanox Technologies Ltd. MSN2010/SA002610, BIOS 5.6.5 08/24/2017
Workqueue: mlxsw_core mlxsw_sp_mr_stats_update [mlxsw_spectrum]
Call Trace:
 <TASK>
 dump_stack_lvl+0xba/0x110
 print_report+0x174/0x4f5
 kasan_report+0xdf/0x110
 mlxsw_sp_mr_stats_update+0x4a5/0x540 drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c:1006 [mlxsw_spectrum]
 process_one_work+0x9cc/0x18e0
 worker_thread+0x5df/0xe40
 kthread+0x3b8/0x730
 ret_from_fork+0x3e9/0x560
 ret_from_fork_asm+0x1a/0x30
 </TASK>

Allocated by task 29933:
 kasan_save_stack+0x30/0x50
 kasan_save_track+0x14/0x30
 __kasan_kmalloc+0x8f/0xa0
 mlxsw_sp_mr_route_add+0xd8/0x4770 [mlxsw_spectrum]
 mlxsw_sp_router_fibmr_event_work+0x371/0xad0 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:7965 [mlxsw_spectrum]
 process_one_work+0x9cc/0x18e0
 worker_thread+0x5df/0xe40
 kthread+0x3b8/0x730
 ret_from_fork+0x3e9/0x560
 ret_from_fork_asm+0x1a/0x30

Freed by task 29933:
 kasan_save_stack+0x30/0x50
 kasan_save_track+0x14/0x30
 __kasan_save_free_info+0x3b/0x70
 __kasan_slab_free+0x43/0x70
 kfree+0x14e/0x700
 mlxsw_sp_mr_route_add+0x2dea/0x4770 drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c:444 [mlxsw_spectrum]
 mlxsw_sp_router_fibmr_event_work+0x371/0xad0 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:7965 [mlxsw_spectrum]
 process_one_work+0x9cc/0x18e0
 worker_thread+0x5df/0xe40
 kthread+0x3b8/0x730
 ret_from_fork+0x3e9/0x560
 ret_from_fork_asm+0x1a/0x30

Fixes: f38656d06725 ("mlxsw: spectrum_mr: Protect multicast route list with a lock")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
---

CC: Jiri Pirko <jiri@resnulli.us>

---
 drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c
index 5afe6b155ef0..81935f87bfcd 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c
@@ -440,7 +440,9 @@ int mlxsw_sp_mr_route_add(struct mlxsw_sp_mr_table *mr_table,
 		rhashtable_remove_fast(&mr_table->route_ht,
 				       &mr_orig_route->ht_node,
 				       mlxsw_sp_mr_route_ht_params);
+		mutex_lock(&mr_table->route_list_lock);
 		list_del(&mr_orig_route->node);
+		mutex_unlock(&mr_table->route_list_lock);
 		mlxsw_sp_mr_route_destroy(mr_table, mr_orig_route);
 	}
 
-- 
2.51.1

Re: [PATCH net 3/3] mlxsw: spectrum_mr: Fix use-after-free when updating multicast route stats

[Simon Horman]

On Tue, Dec 02, 2025 at 06:44:13PM +0100, Petr Machata wrote:
> From: Ido Schimmel <idosch@nvidia.com>
> 
> Cited commit added a dedicated mutex (instead of RTNL) to protect the
> multicast route list, so that it will not change while the driver
> periodically traverses it in order to update the kernel about multicast
> route stats that were queried from the device.
> 
> One instance of list entry deletion (during route replace) was missed
> and it can result in a use-after-free [1].
> 
> Fix by acquiring the mutex before deleting the entry from the list and
> releasing it afterwards.

...

> Fixes: f38656d06725 ("mlxsw: spectrum_mr: Protect multicast route list with a lock")
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
> Reviewed-by: Petr Machata <petrm@nvidia.com>
> Signed-off-by: Petr Machata <petrm@nvidia.com>

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [PATCH net 0/3] mlxsw: Three (m)router fixes

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 2 Dec 2025 18:44:10 +0100 you wrote:
> This patchset contains two fixes in mlxsw Spectrum router code, and one for
> the Spectrum multicast router code. Please see the individual patches for
> more details.
> 
> Ido Schimmel (3):
>   mlxsw: spectrum_router: Fix possible neighbour reference count leak
>   mlxsw: spectrum_router: Fix neighbour use-after-free
>   mlxsw: spectrum_mr: Fix use-after-free when updating multicast route
>     stats
> 
> [...]

Here is the summary with links:
  - [net,1/3] mlxsw: spectrum_router: Fix possible neighbour reference count leak
    https://git.kernel.org/netdev/net/c/b6b638bda240
  - [net,2/3] mlxsw: spectrum_router: Fix neighbour use-after-free
    https://git.kernel.org/netdev/net/c/8b0e69763ef9
  - [net,3/3] mlxsw: spectrum_mr: Fix use-after-free when updating multicast route stats
    https://git.kernel.org/netdev/net/c/8ac1dacec458

You are awesome, thank you!
-- 
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