xen-netback: correctly return errors from netbk_count_requests()

netbk_count_requests() could detect an error, call
netbk_fatal_tx_error() but return 0.  The vif may then be used
afterwards (e.g., in a call to netbk_tx_error().

Since netbk_fatal_tx_error() could set vif->refcnt to 1, the vif may
be freed immediately after the call to netbk_fatal_tx_error() (e.g.,
if the vif is also removed).

Netback thread              Xenwatch thread
-------------------------------------------
netbk_fatal_tx_err()        netback_remove()
                              xenvif_disconnect()
                                ...
                                free_netdev()
netbk_tx_err() Oops!

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reported-by: Christopher S. Aker <caker@theshore.net>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 2b9520c46e97..cd49ba949636 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -911,13 +911,13 @@ static int netbk_count_requests(struct xenvif *vif,
                 if (frags >= work_to_do) {
                         netdev_err(vif->dev, "Need more frags\n");
                         netbk_fatal_tx_err(vif);
-                        return -frags;
+                        return -ENODATA;
                 }
 
                 if (unlikely(frags >= MAX_SKB_FRAGS)) {
                         netdev_err(vif->dev, "Too many frags\n");
                         netbk_fatal_tx_err(vif);
-                        return -frags;
+                        return -E2BIG;
                 }
 
                 memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + frags),
@@ -925,7 +925,7 @@ static int netbk_count_requests(struct xenvif *vif,
                 if (txp->size > first->size) {
                         netdev_err(vif->dev, "Frag is bigger than frame.\n");
                         netbk_fatal_tx_err(vif);
-                        return -frags;
+                        return -EIO;
                 }
 
                 first->size -= txp->size;
@@ -935,7 +935,7 @@ static int netbk_count_requests(struct xenvif *vif,
                         netdev_err(vif->dev, "txp->offset: %x, size: %u\n",
                                  txp->offset, txp->size);
                         netbk_fatal_tx_err(vif);
-                        return -frags;
+                        return -EINVAL;
                 }
         } while ((txp++)->flags & XEN_NETTXF_more_data);
         return frags;