[PATCH net-next] sock: Reset dst when changing sk_mark via setsockopt

[David Barmann]

When setting the SO_MARK socket option, the dst needs to be reset so
that a new route lookup is performed.

This fixes the case where an application wants to change routing by
setting a new sk_mark.  If this is done after some packets have already
been sent, the dst is cached and has no effect.

Signed-off-by: David Barmann <david.barm...@stackpath.com>
---
 net/core/sock.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 6fcc4bc07d19..187badac24a3 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -950,10 +950,14 @@ int sock_setsockopt(struct socket *sock, int level, int 
optname,
                        clear_bit(SOCK_PASSSEC, &sock->flags);
                break;
        case SO_MARK:
-               if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
+               if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)) {
                        ret = -EPERM;
-               else
+               } else {
+                       struct dst_entry *dst = sk_dst_get(sk);
                        sk->sk_mark = val;
+                       sk_dst_reset(sk);
+                       dst_release(dst);
+               }
                break;
 
        case SO_RXQ_OVFL:
-- 
2.14.4