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From:   Bernard Zhao <bernard@vivo.com>
To:     Oliver Neukum <oneukum@suse.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Bernard Zhao <bernard@vivo.com>
Subject: [PATCH] net/usb: potential fix divide error: 0000
Date:   Thu, 21 Oct 2021 23:32:38 -0700
Message-Id: <20211022063238.21800-1-bernard@vivo.com>
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This patch try to fix divide error in drivers/net/usb/usbnet.c.
This bug is reported by google syzbot,
divide error: 0000 [#1] SMP KASAN
CPU: 0 PID: 1315 Comm: kworker/0:6 Not tainted 5.15.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: mld mld_ifc_work
RIP: 0010:usbnet_start_xmit+0x3f1/0x1f70 drivers/net/usb/usbnet.c:1404
Call Trace:
 __netdev_start_xmit include/linux/netdevice.h:4988 [inline]
 netdev_start_xmit include/linux/netdevice.h:5002 [inline]
 xmit_one net/core/dev.c:3576 [inline]
 dev_hard_start_xmit+0x1df/0x890 net/core/dev.c:3592
 sch_direct_xmit+0x25b/0x790 net/sched/sch_generic.c:342
 __dev_xmit_skb net/core/dev.c:3803 [inline]
 __dev_queue_xmit+0xf25/0x2d40 net/core/dev.c:4170
 neigh_resolve_output net/core/neighbour.c:1492 [inline]
 neigh_resolve_output+0x50e/0x820 net/core/neighbour.c:1472
 neigh_output include/net/neighbour.h:510 [inline]
 ip6_finish_output2+0xdbe/0x1b20 net/ipv6/ip6_output.c:126
 __ip6_finish_output.part.0+0x387/0xbb0 net/ipv6/ip6_output.c:191
 __ip6_finish_output include/linux/skbuff.h:982 [inline]
 ip6_finish_output net/ipv6/ip6_output.c:201 [inline]
 NF_HOOK_COND include/linux/netfilter.h:296 [inline]
 ip6_output+0x3d2/0x810 net/ipv6/ip6_output.c:224
 dst_output include/net/dst.h:450 [inline]
 NF_HOOK include/linux/netfilter.h:307 [inline]
 NF_HOOK include/linux/netfilt
the link is:
https://syzkaller.appspot.com/bug?id=e829c15b6c30d4680cf3198f72b0414adc907911

Signed-off-by: Bernard Zhao <bernard@vivo.com>
---
 drivers/net/usb/usbnet.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 840c1c2ab16a..ada1b8242498 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -397,7 +397,7 @@ int usbnet_change_mtu (struct net_device *net, int new_mtu)
 	int		old_rx_urb_size = dev->rx_urb_size;
 
 	// no second zero-length packet read wanted after mtu-sized packets
-	if ((ll_mtu % dev->maxpacket) == 0)
+	if (dev->maxpacket && ((ll_mtu % dev->maxpacket) == 0))
 		return -EDOM;
 	net->mtu = new_mtu;
 
@@ -1401,7 +1401,7 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
 	 * handling ZLP/short packets, so cdc_ncm driver will make short
 	 * packet itself if needed.
 	 */
-	if (length % dev->maxpacket == 0) {
+	if (dev->maxpacket && (length % dev->maxpacket == 0)) {
 		if (!(info->flags & FLAG_SEND_ZLP)) {
 			if (!(info->flags & FLAG_MULTI_PACKET)) {
 				length++;
-- 
2.33.1