[PATCH 5.4 55/67] vxlan: Ensure FDB dump is performed under RCU

Greg Kroah-Hartman
2020-08-10T15:28:54Z

From: Ido Schimmel <idosch@mellanox.com>

[ Upstream commit b5141915b5aec3b29a63db869229e3741ebce258 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/vxlan.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -1225,6 +1225,7 @@ static int vxlan_fdb_dump(struct sk_buff
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;

@@ -1237,12 +1238,15 @@ static int vxlan_fdb_dump(struct sk_buff
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;