CVE-2026-23172: net: wwan: t7xx: fix potential skb->frags overflow in RX path

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

net: wwan: t7xx: fix potential skb->frags overflow in RX path

When receiving data in the DPMAIF RX path, the t7xxdpmaifsetfragtoskb() function adds page fragments to an skb without checking if the number of fragments has exceeded MAXSKBFRAGS. This could lead to a buffer overflow in skbshinfo(skb)->frags[] array, corrupting adjacent memory and potentially causing kernel crashes or other undefined behavior.

This issue was identified through static code analysis by comparing with a similar vulnerability fixed in the mt76 driver commit b102f0c522cf ("mt76: fix array overflow on receiving too many fragments for a packet").

The vulnerability could be triggered if the modem firmware sends packets with excessive fragments. While under normal protocol conditions (MTU 3080 bytes, BAT buffer 3584 bytes), a single packet should not require additional fragments, the kernel should not blindly trust firmware behavior. Malicious, buggy, or compromised firmware could potentially craft packets with more fragments than the kernel expects.

Fix this by adding a bounds check before calling skbaddrxfrag() to ensure nrfrags does not exceed MAXSKBFRAGS.

The check must be performed before unmapping to avoid a page leak and double DMA unmap during device teardown.