[ 123/150] xen-netback: correctly return errors from netbk_count_requests()

Greg Kroah-Hartman
2013-02-27T00:47:52Z

From: David Vrabel <david.vrabel@citrix.com>

[ Upstream commit 35876b5ffc154c357476b2c3bdab10feaf4bd8f0 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/xen-netback/netback.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -911,13 +911,13 @@ static int netbk_count_requests(struct x
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 x
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 x
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;