On Sun, May 24, 2020 at 2:39 PM Ido Schimmel <ido...@idosch.org> wrote:
>
> From: Ido Schimmel <ido...@mellanox.com>
>
> vxlan_fdb_info() is not always called with RTNL held or from an RCU
> read-side critical section. For example, in the following call path:
>
> vxlan_cleanup()
> vxlan_fdb_destroy()
> vxlan_fdb_notify()
> __vxlan_fdb_notify()
> vxlan_fdb_info()
>
> The use of rtnl_dereference() can therefore result in the following
> splat [1].
>
> Fix this by dereferencing the nexthop under RCU read-side critical
> section.
>
> [1]
> [May24 22:56] =============================
> [ +0.004676] WARNING: suspicious RCU usage
> [ +0.004614] 5.7.0-rc5-custom-16219-g201392003491 #2772 Not tainted
> [ +0.007116] -----------------------------
> [ +0.004657] drivers/net/vxlan.c:276 suspicious rcu_dereference_check()
> usage!
> [ +0.008164]
> other info that might help us debug this:
>
> [ +0.009126]
> rcu_scheduler_active = 2, debug_locks = 1
> [ +0.007504] 5 locks held by bash/6892:
> [ +0.004392] #0: ffff8881d47e3410 (&sig->cred_guard_mutex){+.+.}-{3:3}, at:
> __do_execve_file.isra.27+0x392/0x23c0
> [ +0.011795] #1: ffff8881d47e34b0 (&sig->exec_update_mutex){+.+.}-{3:3},
> at: flush_old_exec+0x510/0x2030
> [ +0.010947] #2: ffff8881a141b0b0 (ptlock_ptr(page)#2){+.+.}-{2:2}, at:
> unmap_page_range+0x9c0/0x2590
> [ +0.010585] #3: ffff888230009d50 ((&vxlan->age_timer)){+.-.}-{0:0}, at:
> call_timer_fn+0xe8/0x800
> [ +0.010192] #4: ffff888183729bc8 (&vxlan->hash_lock[h]){+.-.}-{2:2}, at:
> vxlan_cleanup+0x133/0x4a0
> [ +0.010382]
> stack backtrace:
> [ +0.005103] CPU: 1 PID: 6892 Comm: bash Not tainted
> 5.7.0-rc5-custom-16219-g201392003491 #2772
> [ +0.009675] Hardware name: Mellanox Technologies Ltd.
> MSN2100-CB2FO/SA001017, BIOS 5.6.5 06/07/2016
> [ +0.010155] Call Trace:
> [ +0.002775] <IRQ>
> [ +0.002313] dump_stack+0xfd/0x178
> [ +0.003895] lockdep_rcu_suspicious+0x14a/0x153
> [ +0.005157] vxlan_fdb_info+0xe39/0x12a0
> [ +0.004775] __vxlan_fdb_notify+0xb8/0x160
> [ +0.004672] vxlan_fdb_notify+0x8e/0xe0
> [ +0.004370] vxlan_fdb_destroy+0x117/0x330
> [ +0.004662] vxlan_cleanup+0x1aa/0x4a0
> [ +0.004329] call_timer_fn+0x1c4/0x800
> [ +0.004357] run_timer_softirq+0x129d/0x17e0
> [ +0.004762] __do_softirq+0x24c/0xaef
> [ +0.004232] irq_exit+0x167/0x190
> [ +0.003767] smp_apic_timer_interrupt+0x1dd/0x6a0
> [ +0.005340] apic_timer_interrupt+0xf/0x20
> [ +0.004620] </IRQ>
>
> Fixes: 1274e1cc4226 ("vxlan: ecmp support for mac fdb entries")
> Signed-off-by: Ido Schimmel <ido...@mellanox.com>
> Reported-by: Amit Cohen <am...@mellanox.com>
> ---
Acked-by: Roopa Prabhu <ro...@cumulusnetworks.com>
Thanks Ido.
> drivers/net/vxlan.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
> index 3e88fbef2d4a..a0015cdedfaf 100644
> --- a/drivers/net/vxlan.c
> +++ b/drivers/net/vxlan.c
> @@ -263,6 +263,8 @@ static int vxlan_fdb_info(struct sk_buff *skb, struct
> vxlan_dev *vxlan,
> struct nlmsghdr *nlh;
> struct nexthop *nh;
> struct ndmsg *ndm;
> + int nh_family;
> + u32 nh_id;
>
> nlh = nlmsg_put(skb, portid, seq, type, sizeof(*ndm), flags);
> if (nlh == NULL)
> @@ -273,13 +275,20 @@ static int vxlan_fdb_info(struct sk_buff *skb, struct
> vxlan_dev *vxlan,
>
> send_eth = send_ip = true;
>
> - nh = rcu_dereference_rtnl(fdb->nh);
> + rcu_read_lock();
> + nh = rcu_dereference(fdb->nh);
> + if (nh) {
> + nh_family = nexthop_get_family(nh);
> + nh_id = nh->id;
> + }
> + rcu_read_unlock();
> +
> if (type == RTM_GETNEIGH) {
> if (rdst) {
> send_ip = !vxlan_addr_any(&rdst->remote_ip);
> ndm->ndm_family = send_ip ?
> rdst->remote_ip.sa.sa_family : AF_INET;
> } else if (nh) {
> - ndm->ndm_family = nexthop_get_family(nh);
> + ndm->ndm_family = nh_family;
> }
> send_eth = !is_zero_ether_addr(fdb->eth_addr);
> } else
> @@ -299,7 +308,7 @@ static int vxlan_fdb_info(struct sk_buff *skb, struct
> vxlan_dev *vxlan,
> if (send_eth && nla_put(skb, NDA_LLADDR, ETH_ALEN, &fdb->eth_addr))
> goto nla_put_failure;
> if (nh) {
> - if (nla_put_u32(skb, NDA_NH_ID, nh->id))
> + if (nla_put_u32(skb, NDA_NH_ID, nh_id))
> goto nla_put_failure;
> } else if (rdst) {
> if (send_ip && vxlan_nla_put_addr(skb, NDA_DST,
> --
> 2.26.2
>
