netdev - Re: [PATCH net] tipc: block BH before using dst

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Date:   Fri, 22 May 2020 13:56:57 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jon Maloy <jon.maloy@...csson.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] tipc: block BH before using dst_cache

On Fri, May 22, 2020 at 2:30 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> dst_cache_get() documents it must be used with BH disabled.
Interesting, I thought under rcu_read_lock() is enough, which calls
preempt_disable().
have you checked other places where dst_cache_get() are used?

>
> sysbot reported :
>
> BUG: using smp_processor_id() in preemptible [00000000] code: /21697
> caller is dst_cache_get+0x3a/0xb0 net/core/dst_cache.c:68
> CPU: 0 PID: 21697 Comm:  Not tainted 5.7.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x188/0x20d lib/dump_stack.c:118
>  check_preemption_disabled lib/smp_processor_id.c:47 [inline]
>  debug_smp_processor_id.cold+0x88/0x9b lib/smp_processor_id.c:57
>  dst_cache_get+0x3a/0xb0 net/core/dst_cache.c:68
>  tipc_udp_xmit.isra.0+0xb9/0xad0 net/tipc/udp_media.c:164
>  tipc_udp_send_msg+0x3e6/0x490 net/tipc/udp_media.c:244
>  tipc_bearer_xmit_skb+0x1de/0x3f0 net/tipc/bearer.c:526
>  tipc_enable_bearer+0xb2f/0xd60 net/tipc/bearer.c:331
>  __tipc_nl_bearer_enable+0x2bf/0x390 net/tipc/bearer.c:995
>  tipc_nl_bearer_enable+0x1e/0x30 net/tipc/bearer.c:1003
>  genl_family_rcv_msg_doit net/netlink/genetlink.c:673 [inline]
>  genl_family_rcv_msg net/netlink/genetlink.c:718 [inline]
>  genl_rcv_msg+0x627/0xdf0 net/netlink/genetlink.c:735
>  netlink_rcv_skb+0x15a/0x410 net/netlink/af_netlink.c:2469
>  genl_rcv+0x24/0x40 net/netlink/genetlink.c:746
>  netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
>  netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329
>  netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  ____sys_sendmsg+0x6bf/0x7e0 net/socket.c:2362
>  ___sys_sendmsg+0x100/0x170 net/socket.c:2416
>  __sys_sendmsg+0xec/0x1b0 net/socket.c:2449
>  do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
>  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x45ca29
>
> Fixes: e9c1a793210f ("tipc: add dst_cache support for udp media")
> Cc: Xin Long <lucien.xin@...il.com>
> Cc: Jon Maloy <jon.maloy@...csson.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
>  net/tipc/udp_media.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
> index d6620ad535461a4d04ed5ba90569ce8b7df9f994..28a283f26a8dff24d613e6ed57e5e69d894dae66 100644
> --- a/net/tipc/udp_media.c
> +++ b/net/tipc/udp_media.c
> @@ -161,9 +161,11 @@ static int tipc_udp_xmit(struct net *net, struct sk_buff *skb,
>                          struct udp_bearer *ub, struct udp_media_addr *src,
>                          struct udp_media_addr *dst, struct dst_cache *cache)
>  {
> -       struct dst_entry *ndst = dst_cache_get(cache);
> +       struct dst_entry *ndst;
>         int ttl, err = 0;
>
> +       local_bh_disable();
> +       ndst = dst_cache_get(cache);
>         if (dst->proto == htons(ETH_P_IP)) {
>                 struct rtable *rt = (struct rtable *)ndst;
>
> @@ -210,9 +212,11 @@ static int tipc_udp_xmit(struct net *net, struct sk_buff *skb,
>                                            src->port, dst->port, false);
>  #endif
>         }
> +       local_bh_enable();
>         return err;
>
>  tx_error:
> +       local_bh_enable();
>         kfree_skb(skb);
>         return err;
>  }
> --
> 2.27.0.rc0.183.gde8f92d652-goog
>