[PATCH AUTOSEL 4.19 222/237] sock: Reset dst when changing sk_mark via setsockopt

[Sasha Levin <sashal@kernel.org>]

From: David Barmann <david.barmann@stackpath.com>

[ Upstream commit 50254256f382c56bde87d970f3d0d02fdb76ec70 ]

When setting the SO_MARK socket option, if the mark changes, 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.barmann@stackpath.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/core/sock.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index ba4f843cdd1d1..948fd687292a6 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -951,10 +951,12 @@ 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 if (val != sk->sk_mark) {
 			sk->sk_mark = val;
+			sk_dst_reset(sk);
+		}
 		break;
 
 	case SO_RXQ_OVFL:
-- 
2.20.1