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    Subject[PATCH 5.12 458/700] vxlan: add missing rcu_read_lock() in neigh_reduce()
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 85e8b032d6ebb0f698a34dd22c2f13443d905888 ]

    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 <syzkaller@googlegroups.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/net/vxlan.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
    index 53dbc67e8a34..a3ec03ce3343 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;
    }
    --
    2.30.2


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