rds: sysctl: rds_tcp_{rcv,snd}buf: avoid using current->nsproxy

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: rds: sysctl: rds_tcp_{rcv,snd}buf: 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 per-netns structure can be obtained from the table->data using container_of(), then the 'net' one can be retrieved from the listen socket (if available).

References

• https://git.kernel.org/stable/c/de8d6de0ee27be4b2b1e5b06f04aeacbabbba492
• https://git.kernel.org/stable/c/7f5611cbc4871c7fb1ad36c2e5a9edad63dca95c