vxlan: Ensure FDB dump is performed under RCU

The commit cited below removed the RCU read-side critical section from
rtnl_fdb_dump() which means that the ndo_fdb_dump() callback is invoked
without RCU protection.

This results in the following warning [1] in the VXLAN driver, which
relied on the callback being invoked from an RCU read-side critical
section.

Fix this by calling rcu_read_lock() in the VXLAN driver, as already done
in the bridge driver.

[1]
WARNING: suspicious RCU usage
5.8.0-rc4-custom-01521-g481007553ce6 #29 Not tainted
-----------------------------
drivers/net/vxlan.c:1379 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by bridge/166:
 #0: ffffffff85a27850 (rtnl_mutex){+.+.}-{3:3}, at: netlink_dump+0xea/0x1090

stack backtrace:
CPU: 1 PID: 166 Comm: bridge Not tainted 5.8.0-rc4-custom-01521-g481007553ce6 #29
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-2.fc32 04/01/2014
Call Trace:
 dump_stack+0x100/0x184
 lockdep_rcu_suspicious+0x153/0x15d
 vxlan_fdb_dump+0x51e/0x6d0
 rtnl_fdb_dump+0x4dc/0xad0
 netlink_dump+0x540/0x1090
 __netlink_dump_start+0x695/0x950
 rtnetlink_rcv_msg+0x802/0xbd0
 netlink_rcv_skb+0x17a/0x480
 rtnetlink_rcv+0x22/0x30
 netlink_unicast+0x5ae/0x890
 netlink_sendmsg+0x98a/0xf40
 __sys_sendto+0x279/0x3b0
 __x64_sys_sendto+0xe6/0x1a0
 do_syscall_64+0x54/0xa0
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fe14fa2ade0
Code: Bad RIP value.
RSP: 002b:00007fff75bb5b88 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00005614b1ba0020 RCX: 00007fe14fa2ade0
RDX: 000000000000011c RSI: 00007fff75bb5b90 RDI: 0000000000000003
RBP: 00007fff75bb5b90 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00005614b1b89160
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Fixes: 5e6d24358799 ("bridge: netlink dump interface at par with brctl")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 89d85dc..5efe1e2 100644 (file)
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -1376,6 +1376,7 @@ static int vxlan_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb,
        for (h = 0; h < FDB_HASH_SIZE; ++h) {
                struct vxlan_fdb *f;
 
+               rcu_read_lock();
                hlist_for_each_entry_rcu(f, &vxlan->fdb_head[h], hlist) {
                        struct vxlan_rdst *rd;
 
@@ -1387,8 +1388,10 @@ static int vxlan_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb,
                                                     cb->nlh->nlmsg_seq,
                                                     RTM_NEWNEIGH,
                                                     NLM_F_MULTI, NULL);
-                               if (err < 0)
+                               if (err < 0) {
+                                       rcu_read_unlock();
                                        goto out;
+                               }
 skip_nh:
                                *idx += 1;
                                continue;
@@ -1403,12 +1406,15 @@ skip_nh:
                                                     cb->nlh->nlmsg_seq,
                                                     RTM_NEWNEIGH,
                                                     NLM_F_MULTI, rd);
-                               if (err < 0)
+                               if (err < 0) {
+                                       rcu_read_unlock();
                                        goto out;
+                               }
 skip:
                                *idx += 1;
                        }
                }
+               rcu_read_unlock();
        }
 out:
        return err;