Wikipedia
kernel.org is the main distribution point of source code for the Linux kernel, which is the base of the Linux operating system. The website and related infrastructure, which are operated by the Linux Kernel Organization, host the repositories that make all versions of the kernel's source code available to all users. The main purpose of kernel.org is to host repositories used by Linux kernel developers and maintainers of various Linux distributions. Additionally, it hosts various other projects or their mirrors, including the Linux Documentation Project (LDP) and CPAN.
Since August 2014, kernel.org provides additional security by mandating two-factor authentication for commits performed to hosted Git repositories that contain source code of the Linux kernel, with support for both soft tokens and hard tokens.