ipv6: invert flowlabel sharing check in process and user mode

BugLink: https://bugs.launchpad.net/bugs/1830176

[ Upstream commit 95c16925 ]

A request for a flowlabel fails in process or user exclusive mode must
fail if the caller pid or uid does not match. Invert the test.

Previously, the test was unsafe wrt PID recycling, but indeed tested
for inequality: fl1->owner != fl->owner

Fixes: 4f82f457 ("net ip6 flowlabel: Make owner a union of struct pid* and kuid_t")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/ipv6/ip6_flowlabel.c

@@ -639,9 +639,9 @@ int ipv6_flowlabel_opt(struct sock *sk, char __user *optval, int optlen)
 				if (fl1->share == IPV6_FL_S_EXCL ||
 				    fl1->share != fl->share ||
 				    ((fl1->share == IPV6_FL_S_PROCESS) &&
-				     (fl1->owner.pid == fl->owner.pid)) ||
+				     (fl1->owner.pid != fl->owner.pid)) ||
 				    ((fl1->share == IPV6_FL_S_USER) &&
-				     uid_eq(fl1->owner.uid, fl->owner.uid)))
+				     !uid_eq(fl1->owner.uid, fl->owner.uid)))
 					goto release;
 
 				err = -ENOMEM;