net: call sk_dst_reset when set SO_DONTROUTE

BugLink: https://bugs.launchpad.net/bugs/1837477
[ Upstream commit 0fbe82e628c817e292ff588cd5847fc935e025f2 ]

after set SO_DONTROUTE to 1, the IP layer should not route packets if
the dest IP address is not in link scope. But if the socket has cached
the dst_entry, such packets would be routed until the sk_dst_cache
expires. So we should clean the sk_dst_cache when a user set
SO_DONTROUTE option. Below are server/client python scripts which
could reprodue this issue:

server side code:

==========================================================================
import socket
import struct
import time

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('0.0.0.0', 9000))
s.listen(1)
sock, addr = s.accept()
sock.setsockopt(socket.SOL_SOCKET, socket.SO_DONTROUTE, struct.pack('i', 1))
while True:
    sock.send(b'foo')
    time.sleep(1)
==========================================================================

client side code:
==========================================================================
import socket
import time

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('server_address', 9000))
while True:
    data = s.recv(1024)
    print(data)
==========================================================================

Signed-off-by: yupeng <yupeng0921@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/net/core/sock.c b/net/core/sock.c
index b7a42fd73b7f885f307bc037ead8425557a03243..964f6a3b0c258b63c653a137989aabf1791a1aa5 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -735,6 +735,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
                break;
        case SO_DONTROUTE:
                sock_valbool_flag(sk, SOCK_LOCALROUTE, valbool);
+               sk_dst_reset(sk);
                break;
        case SO_BROADCAST:
                sock_valbool_flag(sk, SOCK_BROADCAST, valbool);