usb: gadget: u_ether: fix a potential null pointer dereference

[ Upstream commit 8ae01239609b29ec2eff55967c8e0fe3650cfa09 ]

f_ncm tx timeout can call us with null skb to flush
a pending frame.  In this case skb is NULL to begin
with but ceases to be null after dev->wrap() completes.

In such a case in->maxpacket will be read, even though
we've failed to check that 'in' is not NULL.

Though I've never observed this fail in practice,
however the 'flush operation' simply does not make sense with
a null usb IN endpoint - there's nowhere to flush to...
(note that we're the gadget/device, and IN is from the point
 of view of the host, so here IN actually means outbound...)

Cc: Brooke Basile <brookebasile@gmail.com>
Cc: "Bryan O'Donoghue" <bryan.odonoghue@linaro.org>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Link: https://lore.kernel.org/r/20210701114834.884597-6-zenczykowski@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index 46c50135ef9f7f2aa47c7c3c924245ab9f4092be..4bc95ac3d4485e6e4084f433e32d91f6495387d6 100644 (file)
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -507,8 +507,9 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
        }
        spin_unlock_irqrestore(&dev->lock, flags);
 
-       if (skb && !in) {
-               dev_kfree_skb_any(skb);
+       if (!in) {
+               if (skb)
+                       dev_kfree_skb_any(skb);
                return NETDEV_TX_OK;
        }