UBUNTU-CVE-2026-97964: Medium severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: pppsynctty: ensure a writeable skb header pppsynctxmunge() checks headroom before prepending the address and control bytes, but does not ensure that the skb header is writable. A received skb can reach this function through PPP channel bridging without passing through pppstartxmit(), which calls skbcowhead(). For example, a PPPoE frame may share its buffer with a clone queued to an AFPACKET socket. If it is bridged to a synchronous tty channel, the address/control bytes can overwrite data still visible to that socket. Use skbcowhead() to ensure both sufficient headroom and a writable header.