Re: [PATCH net] vxlan: add missing rcu_read_lock() in neigh_reduce()
From: Daniel Borkmann <daniel@iogearbox.net>
Date: 2021-06-21 16:04:53
On 6/21/21 4:44 PM, Eric Dumazet wrote:
From: Eric Dumazet <edumazet@google.com>
syzbot complained in neigh_reduce(), because rcu_read_lock_bh()
is treated differently than rcu_read_lock()
WARNING: suspicious RCU usage
5.13.0-rc6-syzkaller #0 Not tainted
-----------------------------
include/net/addrconf.h:313 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
3 locks held by kworker/0:0/5:
#0: ffff888011064d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff888011064d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
#0: ffff888011064d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
#0: ffff888011064d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:617 [inline]
#0: ffff888011064d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: ffff888011064d38 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x871/0x1600 kernel/workqueue.c:2247
#1: ffffc90000ca7da8 ((work_completion)(&port->wq)){+.+.}-{0:0}, at: process_one_work+0x8a5/0x1600 kernel/workqueue.c:2251
#2: ffffffff8bf795c0 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x1da/0x3130 net/core/dev.c:4180
stack backtrace:
CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.13.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events ipvlan_process_multicast
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
__in6_dev_get include/net/addrconf.h:313 [inline]
__in6_dev_get include/net/addrconf.h:311 [inline]
neigh_reduce drivers/net/vxlan.c:2167 [inline]
vxlan_xmit+0x34d5/0x4c30 drivers/net/vxlan.c:2919
__netdev_start_xmit include/linux/netdevice.h:4944 [inline]
netdev_start_xmit include/linux/netdevice.h:4958 [inline]
xmit_one net/core/dev.c:3654 [inline]
dev_hard_start_xmit+0x1eb/0x920 net/core/dev.c:3670
__dev_queue_xmit+0x2133/0x3130 net/core/dev.c:4246
ipvlan_process_multicast+0xa99/0xd70 drivers/net/ipvlan/ipvlan_core.c:287
process_one_work+0x98d/0x1600 kernel/workqueue.c:2276
worker_thread+0x64c/0x1120 kernel/workqueue.c:2422
kthread+0x3b1/0x4a0 kernel/kthread.c:313
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Fixes: f564f45c4518 ("vxlan: add ipv6 proxy support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <redacted>[ +Paul/Toke ] Only a side comment on this fix given the series under [0] where we remove the rcu_read_lock() given covered by rcu_read_lock_bh(): [...] It seems [1] that back in the early days of XDP, local_bh_disable() did not provide RCU protection, which is why the rcu_read_lock() calls were added to drivers in the first place. But according to Paul [2], in recent kernels a local_bh_disable()/local_bh_enable() pair functions as one big RCU read-side section, so no further protection is needed. This even applies to -rt kernels, which has an explicit rcu_read_lock() in place as part of the local_bh_disable() [3]. [...] Paul/Toke, with regards to related questions under [1], I presume there should additionally be a fixup for lockdep /in general/ to silence warning like these ? [0] https://lore.kernel.org/bpf/20210617212748.32456-1-toke@redhat.com/ (local) [1] https://lore.kernel.org/bpf/1881ecbe-06ec-6b0a-836c-033c31fabef4@iogearbox.net/ (local)
quoted hunk ↗ jump to hunk
--- drivers/net/vxlan.c | 2 ++ 1 file changed, 2 insertions(+)diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c index 02a14f1b938ad50fc28044b7670ba5f6bf924345..5a8df5a195cb5700c45b4785355ef8ed84866052 100644 --- a/drivers/net/vxlan.c +++ b/drivers/net/vxlan.c@@ -2164,6 +2164,7 @@ static int neigh_reduce(struct net_device *dev, struct sk_buff *skb, __be32 vni) struct neighbour *n; struct nd_msg *msg; + rcu_read_lock(); in6_dev = __in6_dev_get(dev); if (!in6_dev) goto out;@@ -2215,6 +2216,7 @@ static int neigh_reduce(struct net_device *dev, struct sk_buff *skb, __be32 vni) } out: + rcu_read_unlock(); consume_skb(skb); return NETDEV_TX_OK; }