mptcp: fix sk_forward_memory corruption on retransmission

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix sk_forward_memory corruption on retransmission MPTCP sk_forward_memory handling is a bit special, as such field is protected by the msk socket spin_lock, instead of the plain socket lock. Currently we have a code path updating such field without handling the relevant lock: __mptcp_retrans() -> __mptcp_clean_una_wakeup() Several helpers in __mptcp_clean_una_wakeup() will update sk_forward_alloc, possibly causing such field corruption, as reported by Matthieu. Address the issue providing and using a new variant of blamed function which explicitly acquires the msk spin lock.

References

• https://git.kernel.org/stable/c/b9c78b1a95966a7bd2ddae05b73eafc0cda4fba3
• https://git.kernel.org/stable/c/b5941f066b4ca331db225a976dae1d6ca8cf0ae3