mt7925_usb_sdio_tx_prepare_skb() pushes a TX descriptor and a USB header onto every skb and assumes the headroom for them is already there. That holds for locally generated traffic, where mac80211 reserves hw->extra_tx_headroom, but forwarded frames are sent through ieee80211_8023_xmit(), which does not reserve it. Bridge a wired interface to an mt7925u AP and the first forwarded frame that arrives short panics the kernel: skbuff: skb_under_panic: len:415 put:4 tail:0x19b end:0x640 dev:wlan1 kernel BUG at net/core/skbuff.c:212! Call trace: skb_panic+0x58/0x60 (P) skb_push+0x58/0x60 mt7925_usb_sdio_tx_prepare_skb+0xf8/0x1b8 [mt7925_common] mt76u_tx_queue_skb+0xa0/0x1f8 [mt76_usb] __mt76_tx_queue_skb+0x54/0xe8 [mt76] mt76_txq_schedule.part.0+0x204/0x478 [mt76] mt76_txq_schedule_all+0x50/0x80 [mt76] mt792x_tx_worker+0x68/0x100 [mt792x_lib] __mt76_worker_fn+0x84/0x150 [mt76] Whether a given setup hits it depends on how much headroom the ingress netdev leaves in its rx skbs. Reproduced on a Raspberry Pi 5 bridging onboard ethernet to a Netgear A9000; originally reported on an MT7986 router running OpenWrt. Nick Morrow's testing on a Pi 4 (bcmgenet), which leaves more headroom, helped narrow the trigger to the ingress path. The same bug was fixed on mt7921 by commit 98c4d0abf5c4 ("mt76: mt7921: don't assume adequate headroom for SDIO headers"), but mt7925 was copied from mt7921 without the fix. Add the same guard here. Fixes: c948b5da6bbe ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips") Cc: stable@vger.kernel.org Link: https://github.com/morrownr/mt76/issues/52 Signed-off-by: Devin Wittmayer --- drivers/net/wireless/mediatek/mt76/mt7925/mac.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c index 0641a7131d7c..a515147a6ccf 100644 --- a/drivers/net/wireless/mediatek/mt76/mt7925/mac.c +++ b/drivers/net/wireless/mediatek/mt76/mt7925/mac.c @@ -1427,6 +1427,10 @@ int mt7925_usb_sdio_tx_prepare_skb(struct mt76_dev *mdev, void *txwi_ptr, if (!wcid) wcid = &dev->mt76.global_wcid; + err = skb_cow_head(skb, MT_SDIO_TXD_SIZE + MT_SDIO_HDR_SIZE); + if (err) + return err; + if (sta) { struct mt792x_sta *msta = (struct mt792x_sta *)sta->drv_priv; -- 2.55.0