CVE-2026-98827: wifi: ath9k_htc: bound TX aggregation to MAX_TX_BUF_SIZE

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

wifi: ath9khtc: bound TX aggregation to MAXTXBUFSIZE

hifusbtx() dequeues up to MAXTXAGGRNUM (20) frames into a single txbuf of MAXTXBUFSIZE (32768) bytes, limiting the batch by record count but never by cumulative byte length.

With large frames (MTU 2304), 20 aggregated frames of 2292 bytes each exceed the allocation (20 2296 = 45920 bytes), so the memcpy() in the loop writes up to 13152 bytes past txbuf->buf before usbsubmiturb().

Peek the queue head and stop before copying any record that would cross MAXTXBUFSIZE, then dispatch the current batch. Leftover skbs remain queued and are drained on the next URB completion.

The byte bound changes the loop's exit semantics: it can now exit before i == txskbcnt - 1. Stock only finalized txbuf->len on that last index (len += offset), so an early break would submit a URB holding only the last record's length while every dequeued skb is freed on completion, silently dropping frames. Make txbuf->len a running total and advance txbuf->offset per record instead; the stride roundup(nskb->len + 4, 4) is identical to the stock stride when the loop runs to completion.

Tested on hardware with an MTU 2304 flood: the loop stops at record 15 (len = 32144, offset = 32144, within 32768), no oversized URB is submitted, and MTU 1500 pings pass 20/20.