[PATCH 6.12 051/567] mlxsw: spectrum_mr: Fix use-after-free when updating multicast route stats

Greg Kroah-Hartman
2026-01-06T17:17:05Z

From: Ido Schimmel <idosch@nvidia.com>

[ Upstream commit 8ac1dacec458f55f871f7153242ed6ab60373b90 ]

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>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/f996feecfd59fde297964bfc85040b6d83ec6089.1764695650.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 5afe6b155ef0d..81935f87bfcd7 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);
}

--
2.51.0