linux-kernel - [PATCH 3.16 15/47] usb: gadget: ether: Fix race between gether_disconnect and rx

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Date:   Fri, 25 Oct 2019 19:03:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Felipe Balbi" <felipe.balbi@...ux.intel.com>,
        "Kiruthika Varadarajan" <Kiruthika.Varadarajan@...man.com>
Subject: [PATCH 3.16 15/47] usb: gadget: ether: Fix race between
 gether_disconnect and rx_submit

3.16.76-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Kiruthika Varadarajan <Kiruthika.Varadarajan@...man.com>

commit d29fcf7078bc8be2b6366cbd4418265b53c94fac upstream.

On spin lock release in rx_submit, gether_disconnect get a chance to
run, it makes port_usb NULL, rx_submit access NULL port USB, hence null
pointer crash.

Fixed by releasing the lock in rx_submit after port_usb is used.

Fixes: 2b3d942c4878 ("usb ethernet gadget: split out network core")
Signed-off-by: Kiruthika Varadarajan <Kiruthika.Varadarajan@...man.com>
Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/gadget/u_ether.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/usb/gadget/u_ether.c
+++ b/drivers/usb/gadget/u_ether.c
@@ -202,11 +202,12 @@ rx_submit(struct eth_dev *dev, struct us
 		out = dev->port_usb->out_ep;
 	else
 		out = NULL;
-	spin_unlock_irqrestore(&dev->lock, flags);
 
 	if (!out)
+	{
+		spin_unlock_irqrestore(&dev->lock, flags);
 		return -ENOTCONN;
-
+	}
 
 	/* Padding up to RX_EXTRA handles minor disagreements with host.
 	 * Normally we use the USB "terminate on short read" convention;
@@ -227,6 +228,7 @@ rx_submit(struct eth_dev *dev, struct us
 
 	if (dev->port_usb->is_fixed)
 		size = max_t(size_t, size, dev->port_usb->fixed_out_len);
+	spin_unlock_irqrestore(&dev->lock, flags);
 
 	skb = alloc_skb(size + NET_IP_ALIGN, gfp_flags);
 	if (skb == NULL) {