CVE-2026-98711: wifi: cw1200: fix TX padding OOB read leaking heap data to device

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

wifi: cw1200: fix TX padding OOB read leaking heap data to device

The TX path rounds the transfer size up to the bus alignment (alignsize(), up to 511 bytes for SDIO, 1 byte for SPI) but sends the padded length straight from the frame buffer, which has no room reserved for the padding. cw1200datawrite() therefore reads past the end of the frame and the bus transfer carries those bytes to the device. A bogus device can collect up to 511 bytes of kernel heap data per TX frame.

The RX path does not have this problem: it allocates the skb with the aligned length (alloclen) before reading.

Compute the exact padding with the bus alignsize() callback, make sure queued TX frames have tailroom for it, and zero the padding bytes before the transfer so nothing past the frame is exposed.

This is not expected to change driver behavior on most cases: frame contents and transfer sizes are unchanged, only the content of the padding bytes (previously undefined stale memory, now zero), which the device never reads since the WSM header carries the real frame length. The skb expansion can only fail under memory exhaustion, in which case the frame is dropped like on the existing error paths of cw1200tx().

Discovered by Atuin - Automated Vulnerability Discovery Engine.