From 7387dbbcdb2404e189591435527dcc65463819d7 Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Wed, 12 Jul 2017 09:12:53 +0200 Subject: [PATCH] mlxsw: spectrum_router: Fix use-after-free in route replace While working on IPv6 route replace I realized we can have a use-after-free in IPv4 in case the replaced route is offloaded and the only one using its FIB info. The problem is that fib_table_insert() drops the reference on the FIB info of the replaced routes which is eventually freed via call_rcu(). Since the driver doesn't hold a reference on this FIB info it can cause a use-after-free when it tries to clear the RTNH_F_OFFLOAD flag stored in fi->fib_flags. After running the following commands in a loop for enough time with a KASAN enabled kernel I finally got the below trace. $ ip route add 192.168.50.0/24 via 192.168.200.1 dev enp3s0np3 $ ip route replace 192.168.50.0/24 dev enp3s0np5 $ ip route del 192.168.50.0/24 dev enp3s0np5 BUG: KASAN: use-after-free in mlxsw_sp_fib_entry_offload_unset+0xa7/0x120 [mlxsw_spectrum] Read of size 4 at addr ffff8803717d9820 by task kworker/u4:2/55 [...] ? mlxsw_sp_fib_entry_offload_unset+0xa7/0x120 [mlxsw_spectrum] ? mlxsw_sp_fib_entry_offload_unset+0xa7/0x120 [mlxsw_spectrum] ? mlxsw_sp_router_neighs_update_work+0x1cd0/0x1ce0 [mlxsw_spectrum] ? mlxsw_sp_fib_entry_offload_unset+0xa7/0x120 [mlxsw_spectrum] __asan_load4+0x61/0x80 mlxsw_sp_fib_entry_offload_unset+0xa7/0x120 [mlxsw_spectrum] mlxsw_sp_fib_entry_offload_refresh+0xb6/0x370 [mlxsw_spectrum] mlxsw_sp_router_fib_event_work+0xd1c/0x2780 [mlxsw_spectrum] [...] Freed by task 5131: save_stack_trace+0x16/0x20 save_stack+0x46/0xd0 kasan_slab_free+0x70/0xc0 kfree+0x144/0x570 free_fib_info_rcu+0x2e7/0x410 rcu_process_callbacks+0x4f8/0xe30 __do_softirq+0x1d3/0x9e2 Fix this by taking a reference on the FIB info when creating the nexthop group it represents and drop it when the group is destroyed. Fixes: 599cf8f95f22 ("mlxsw: spectrum_router: Add support for route replace") Signed-off-by: Ido Schimmel Signed-off-by: Jiri Pirko Signed-off-by: David S. Miller --- drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c index 129afc168fd9..383fef5a8e24 100644 --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c @@ -1867,6 +1867,7 @@ mlxsw_sp_nexthop_group_create(struct mlxsw_sp *mlxsw_sp, struct fib_info *fi) nh_grp->gateway = fi->fib_nh->nh_scope == RT_SCOPE_LINK; nh_grp->count = fi->fib_nhs; nh_grp->key.fi = fi; + fib_info_hold(fi); for (i = 0; i < nh_grp->count; i++) { nh = &nh_grp->nexthops[i]; fib_nh = &fi->fib_nh[i]; @@ -1886,6 +1887,7 @@ err_nexthop_init: nh = &nh_grp->nexthops[i]; mlxsw_sp_nexthop_fini(mlxsw_sp, nh); } + fib_info_put(nh_grp->key.fi); kfree(nh_grp); return ERR_PTR(err); } @@ -1904,6 +1906,7 @@ mlxsw_sp_nexthop_group_destroy(struct mlxsw_sp *mlxsw_sp, } mlxsw_sp_nexthop_group_refresh(mlxsw_sp, nh_grp); WARN_ON_ONCE(nh_grp->adj_index_valid); + fib_info_put(nh_grp->key.fi); kfree(nh_grp); }