Openwall Project: Linux kernel patch from the Openwall Project

"This patch is a collection of security-related features for the Linux kernel, all configurable via the new 'Security options' configuration section. In addition to the new features, some versions of the patch contain various security fixes. The number of such fixes changes from version to version, as some are becoming obsolete (such as because of the same problem getting fixed with a new kernel release), while other security issues are discovered."

"Most buffer overflow exploits are based on overwriting a function's return address on the stack to point to some arbitrary code, which is also put onto the stack. If the stack area is non-executable, buffer overflow vulnerabilities become harder to exploit."

"Another way to exploit a buffer overflow is to point the return address to a function in libc, usually system(). This patch also changes the default address that shared libraries are mmap()'ed at to make it always contain a zero byte. This makes it impossible to specify any more data (parameters to the function, or more copies of the return address when filling with a pattern), -- in many exploits that have to do with ASCIIZ strings."

"However, note that this patch is by no means a complete solution, it just adds an extra layer of security. Many buffer overflow vulnerabilities will remain exploitable a more complicated way, and some will even remain unaffected by the patch. The reason for using such a patch is to protect against some of the buffer overflow vulnerabilities that are yet unknown."

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