net/appletalk: fix minor pointer leak to userspace in SIOCFINDIPDDPRT

Fields ->dev and ->next of struct ipddp_route may be copied to
userspace on the SIOCFINDIPDDPRT ioctl. This is only accessible
to CAP_NET_ADMIN though. Let's manually copy the relevant fields
instead of using memcpy().

BugLink: http://blog.infosectcbr.com.au/2018/09/linux-kernel-infoleaks.html
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/net/appletalk/ipddp.c b/drivers/net/appletalk/ipddp.c
index 9375cef22420..3d27616d9c85 100644
--- a/drivers/net/appletalk/ipddp.c
+++ b/drivers/net/appletalk/ipddp.c
@@ -283,8 +283,12 @@ static int ipddp_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
                 case SIOCFINDIPDDPRT:
                         spin_lock_bh(&ipddp_route_lock);
                         rp = __ipddp_find_route(&rcp);
-                        if (rp)
-                                memcpy(&rcp2, rp, sizeof(rcp2));
+                        if (rp) {
+                                memset(&rcp2, 0, sizeof(rcp2));
+                                rcp2.ip    = rp->ip;
+                                rcp2.at    = rp->at;
+                                rcp2.flags = rp->flags;
+                        }
                         spin_unlock_bh(&ipddp_route_lock);
 
                         if (rp) {