diff options
| author | Laurent Vivier <lvivier@redhat.com> | 2026-07-31 11:27:11 +0200 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-08-04 18:17:20 -0700 |
| commit | 1505b2cb6ae1c7e8ac0c6e4590a204ffc3ab2b24 (patch) | |
| tree | 820e46281e3d26410c7a2e2c63cc81e296b5c7d5 /drivers | |
| parent | 2cbd8a4e5e09aa232a1f8d56ce3d070b18ab2b10 (diff) | |
usbnet: cap max_mtu for drivers without bind callback
usbnet_probe() initializes max_mtu to ETH_MAX_MTU and only caps it
inside the if (info->bind) block. Drivers without a bind callback
never enter this block, so max_mtu stays at ETH_MAX_MTU.
QEMU's usb-net device (0x0525/0xa4a2) is claimed by the cdc_subset
driver which has no bind callback. The guest accepts any MTU from DHCP
(e.g. 65520 from passt), leading to TCP segments that exceed the
device's 2048-byte receive buffer and are silently dropped.
Initialize max_mtu to net->mtu at probe time and update it inside
the bind block.
Fixes: f77f0aee4da4 ("net: use core MTU range checking in USB NIC drivers")
Cc: jarod@redhat.com
Cc: stable@vger.kernel.org
Link: https://gitlab.com/qemu-project/qemu/-/issues/3268
Link: https://bugs.passt.top/show_bug.cgi?id=189
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Link: https://patch.msgid.link/20260731092711.857684-1-lvivier@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/net/usb/usbnet.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index 25518635b7b7..a19ecf718f36 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -1794,7 +1794,7 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod) */ dev->hard_mtu = net->mtu + net->hard_header_len; net->min_mtu = 0; - net->max_mtu = ETH_MAX_MTU; + net->max_mtu = net->mtu; net->netdev_ops = &usbnet_netdev_ops; net->watchdog_timeo = TX_TIMEOUT_JIFFIES; @@ -1804,6 +1804,7 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod) // allow device-specific bind/init procedures // NOTE net->name still not usable ... if (info->bind) { + net->max_mtu = ETH_MAX_MTU; status = info->bind(dev, udev); if (status < 0) goto out1; |