CVE-2025-21641

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

mptcp: sysctl: blackhole timeout: avoid using current->nsproxy

As mentioned in the previous commit, using the 'net' structure via
'current' is not recommended for different reasons:

- Inconsistency: getting info from the reader's/writer's netns vs only
  from the opener's netns.

- current->nsproxy can be NULL in some cases, resulting in an 'Oops'
  (null-ptr-deref), e.g. when the current task is exiting, as spotted by
  syzbot [1] using acct(2).

The 'pernet' structure can be obtained from the table->data using
container_of().