On Fri, May 22, 2020 at 2:30 AM Eric Dumazet <eduma...@google.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....@gmail.com>
> Cc: Jon Maloy <jon.ma...@ericsson.com>
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Reported-by: syzbot <syzkal...@googlegroups.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
>
