Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

mt76: mt7921: don't assume adequate headroom for SDIO headers

mt7921_usb_sdio_tx_prepare_skb() calls mt7921_usb_sdio_write_txwi() and mt7921_skb_add_usb_sdio_hdr(), both of which blindly assume that adequate headroom will be available in the passed skb. This assumption typically is satisfied when the skb was allocated in the net core for transmission via the mt7921 netdev (although even that is only an optimization and is not strictly guaranteed), but the assumption is sometimes not satisfied when the skb originated in the receive path of another netdev and was passed through to the mt7921, such as by the bridge layer. Blindly prepending bytes to an skb is always wrong.

This commit introduces a call to skb_cow_head() before the call to mt7921_usb_sdio_write_txwi() in mt7921_usb_sdio_tx_prepare_skb() to ensure that at least MT_SDIO_TXD_SIZE + MT_SDIO_HDR_SIZE bytes can be pushed onto the skb.

Without this fix, I can trivially cause kernel panics by bridging an MT7921AU-based USB 802.11ax interface with an Ethernet interface on an Intel Atom-based x86 system using its onboard RTL8169 PCI Ethernet adapter and also on an ARM-based Raspberry Pi 1 using its onboard SMSC9512 USB Ethernet adapter. Note that the panics do not occur in every system configuration, as they occur only if the receiving netdev leaves less headroom in its received skbs than the mt7921 needs for its SDIO headers.

Here is an example stac…