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CDC-NCM: handle incomplete transfer of MTU
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A malicious device may give half an answer when asked
for its MTU. The driver will proceed after this with
a garbage MTU. Anything but a complete answer must be treated
as an error.

V2: used sizeof as request by Alexander

Reported-and-tested-by: syzbot+0631d878823ce2411636@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Oliver Neukum authored and David S. Miller committed Nov 7, 2019
1 parent 025ec40 commit 332f989
Showing 1 changed file with 3 additions and 3 deletions.
6 changes: 3 additions & 3 deletions drivers/net/usb/cdc_ncm.c
Original file line number Diff line number Diff line change
Expand Up @@ -578,8 +578,8 @@ static void cdc_ncm_set_dgram_size(struct usbnet *dev, int new_size)
/* read current mtu value from device */
err = usbnet_read_cmd(dev, USB_CDC_GET_MAX_DATAGRAM_SIZE,
USB_TYPE_CLASS | USB_DIR_IN | USB_RECIP_INTERFACE,
0, iface_no, &max_datagram_size, 2);
if (err < 0) {
0, iface_no, &max_datagram_size, sizeof(max_datagram_size));
if (err < sizeof(max_datagram_size)) {
dev_dbg(&dev->intf->dev, "GET_MAX_DATAGRAM_SIZE failed\n");
goto out;
}
Expand All @@ -590,7 +590,7 @@ static void cdc_ncm_set_dgram_size(struct usbnet *dev, int new_size)
max_datagram_size = cpu_to_le16(ctx->max_datagram_size);
err = usbnet_write_cmd(dev, USB_CDC_SET_MAX_DATAGRAM_SIZE,
USB_TYPE_CLASS | USB_DIR_OUT | USB_RECIP_INTERFACE,
0, iface_no, &max_datagram_size, 2);
0, iface_no, &max_datagram_size, sizeof(max_datagram_size));
if (err < 0)
dev_dbg(&dev->intf->dev, "SET_MAX_DATAGRAM_SIZE failed\n");

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