sctp: sysctl: plpmtud_probe_interval: avoid using current->nsproxy

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sctp: sysctl: plpmtud_probe_interval: avoid using current->nsproxy As mentioned in a previous commit of this series, 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 'net' structure can be obtained from the table->data using container_of(). Note that table->data could also be used directly, as this is the only member needed from the 'net' structure, but that would increase the size of this fix, to use '*data' everywhere 'net->sctp.probe_interval' is used.

References

• https://git.kernel.org/stable/c/1dc5da6c4178f3e4b95c631418f72de9f86c0449
• https://git.kernel.org/stable/c/44ee8635922b6eb940faddb961a8347c6857d722
• https://git.kernel.org/stable/c/284a221f8fa503628432c7bb5108277c688c6ffa
• https://git.kernel.org/stable/c/bcf8c60074e81ed2ac2d35130917175a3949c917
• https://git.kernel.org/stable/c/6259d2484d0ceff42245d1f09cc8cb6ee72d847a