[SRU][Cosmic][Bionic][Xenial][PATCH 2/2] net/af_iucv: fix skb handling on HiperTransport xmit error

[Frank Heimes]

From: Julian Wiedmann <jwi at linux.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1800639

    net/af_iucv: fix skb handling on HiperTransport xmit error

    When sending an skb, afiucv_hs_send() bails out on various error
    conditions. But currently the caller has no way of telling whether the
    skb was freed or not - resulting in potentially either
    a) leaked skbs from iucv_send_ctrl(), or
    b) double-free's from iucv_sock_sendmsg().

    As dev_queue_xmit() will always consume the skb (even on error), be
    consistent and also free the skb from all other error paths. This way
    callers no longer need to care about managing the skb.

    Signed-off-by: Julian Wiedmann <jwi at linux.ibm.com>
    Reviewed-by: Ursula Braun <ubraun at linux.ibm.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>

---

diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index 01000c1..e2f16a0 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -351,20 +351,28 @@ static int afiucv_hs_send(struct iucv_message *imsg,
struct sock *sock,
                memcpy(&phs_hdr->iucv_hdr, imsg, sizeof(struct
iucv_message));

        skb->dev = iucv->hs_dev;
-       if (!skb->dev)
-               return -ENODEV;
-       if (!(skb->dev->flags & IFF_UP) || !netif_carrier_ok(skb->dev))
-               return -ENETDOWN;
+       if (!skb->dev) {
+               err = -ENODEV;
+               goto err_free;
+       }
+       if (!(skb->dev->flags & IFF_UP) || !netif_carrier_ok(skb->dev)) {
+               err = -ENETDOWN;
+               goto err_free;
+       }
        if (skb->len > skb->dev->mtu) {
-               if (sock->sk_type == SOCK_SEQPACKET)
-                       return -EMSGSIZE;
-               else
-                       skb_trim(skb, skb->dev->mtu);
+               if (sock->sk_type == SOCK_SEQPACKET) {
+                       err = -EMSGSIZE;
+                       goto err_free;
+               }
+               skb_trim(skb, skb->dev->mtu);
        }
        skb->protocol = cpu_to_be16(ETH_P_AF_IUCV);
        nskb = skb_clone(skb, GFP_ATOMIC);
-       if (!nskb)
-               return -ENOMEM;
+       if (!nskb) {
+               err = -ENOMEM;
+               goto err_free;
+       }
+
        skb_queue_tail(&iucv->send_skb_q, nskb);
        err = dev_queue_xmit(skb);
        if (net_xmit_eval(err)) {
@@ -375,6 +383,10 @@ static int afiucv_hs_send(struct iucv_message *imsg,
struct sock *sock,
                WARN_ON(atomic_read(&iucv->msg_recv) < 0);
        }
        return net_xmit_eval(err);
+
+err_free:
+       kfree_skb(skb);
+       return err;
 }

 static struct sock *__iucv_get_sock_by_name(char *nm)
@@ -1167,7 +1179,7 @@ static int iucv_sock_sendmsg(struct socket *sock,
struct msghdr *msg,
                err = afiucv_hs_send(&txmsg, sk, skb, 0);
                if (err) {
                        atomic_dec(&iucv->msg_sent);
-                       goto fail;
+                       goto out;
                }
        } else { /* Classic VM IUCV transport */
                skb_queue_tail(&iucv->send_skb_q, skb);
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