[PATCH net-next 2/8] net: cdc_ncm: always reallocate tx_curr_skb when tx_max increases

We are calling usbnet_start_xmit() to flush any remaining data,
depending on the side effect that tx_curr_skb is set to NULL,
ensuring a new allocation using the updated tx_max.  But this
side effect will only happen if there were any cached data ready
to transmit. If not, then an empty tx_curr_skb is still allocated
using the old tx_max size. Free it to avoid a buffer overrun.

Fixes: 68864abf08f0 ("net: cdc_ncm: support rx_max/tx_max updates when running")
Signed-off-by: Bjørn Mork <redacted>
---
 drivers/net/usb/cdc_ncm.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 2bbbd65591c7..ff5b3a854898 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c

@@ -268,6 +268,11 @@ static void cdc_ncm_update_rxtx_max(struct usbnet *dev, u32 new_rx, u32 new_tx)
 	if (netif_running(dev->net) && val > ctx->tx_max) {
 		netif_tx_lock_bh(dev->net);
 		usbnet_start_xmit(NULL, dev->net);
+		/* make sure tx_curr_skb is reallocated if it was empty */
+		if (ctx->tx_curr_skb) {
+			dev_kfree_skb_any(ctx->tx_curr_skb);
+			ctx->tx_curr_skb = NULL;
+		}
 		ctx->tx_max = val;
 		netif_tx_unlock_bh(dev->net);
 	} else {

-- 
2.0.0.rc4

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