sunrpc: fix client side handling of tls alerts

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sunrpc: fix client side handling of tls alerts A security exploit was discovered in NFS over TLS in tls_alert_recv due to its assumption that there is valid data in the msghdr's iterator's kvec. Instead, this patch proposes the rework how control messages are setup and used by sock_recvmsg(). If no control message structure is setup, kTLS layer will read and process TLS data record types. As soon as it encounters a TLS control message, it would return an error. At that point, NFS can setup a kvec backed control buffer and read in the control message such as a TLS alert. Scott found that a msg iterator can advance the kvec pointer as a part of the copy process thus we need to revert the iterator before calling into the tls_alert_recv.

References

• https://git.kernel.org/stable/c/a55b3d15331859d9fdd261cfa6d34ca2aeb0fb95
• https://git.kernel.org/stable/c/c36b2fbd60e8f9c6f975522130998608880c93be
• https://git.kernel.org/stable/c/3ee397eaaca4fa04db21bb98c8f1d0c6cc525368
• https://git.kernel.org/stable/c/3feada5baf4dc96e151ff2ca54630e1d274e5458
• https://git.kernel.org/stable/c/cc5d59081fa26506d02de2127ab822f40d88bc5a