net: arp_ioctl() must hold RTNL

Commit 941666c2e3e0 "net: RCU conversion of dev_getbyhwaddr() and
arp_ioctl()" introduced a regression, reported by Jamie Heilman.
"arp -Ds 192.168.2.41 eth0 pub" triggered the ASSERT_RTNL() assert
in pneigh_lookup()

Removing RTNL requirement from arp_ioctl() was a mistake, just revert
that part.

Reported-by: Jamie Heilman <jamie@audible.transient.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 8393ec408cd4..1e5077d2cca6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -749,7 +749,8 @@ EXPORT_SYMBOL(dev_get_by_index);
  *      @ha: hardware address
  *
  *      Search for an interface by MAC address. Returns NULL if the device
- *      is not found or a pointer to the device. The caller must hold RCU
+ *      is not found or a pointer to the device.
+ *      The caller must hold RCU or RTNL.
  *      The returned device has not had its ref count increased
  *      and the caller must therefore be careful about locking
  *