CVE-2021-47132

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.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.