[PATCH 127/139] xen-netback: correctly return errors from netbk_count_requests()

[Luis Henriques]

3.5.7.7 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Vrabel <david.vrabel@xxxxxxxxxx>

commit 35876b5ffc154c357476b2c3bdab10feaf4bd8f0 upstream.

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@xxxxxxxxxx>
Signed-off-by: Jan Beulich <JBeulich@xxxxxxxx>
Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Reported-by: Christopher S. Aker <caker@xxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 drivers/net/xen-netback/netback.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index f3c3a68..a98f012 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -882,13 +882,13 @@ 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),
@@ -896,7 +896,7 @@ 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;
@@ -906,7 +906,7 @@ 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;
-- 
1.8.1.2

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