On Thu, 14 Aug 2003, Stephen Clowater wrote: > Also, you can use chpax, and turn on a non-executable stack, and with a small > amount of voodoo (in tracking down the binarys and .so's that need the stack, > wich typically is only a single binary or .so file, wich you can find with > ptrace, strace, or ltrace) you can have all of your stuff run with a > non-executeable stack, thus making stack smashing impossible. Nothing can > execute off your stack so a malicous person can override all the addresses he > wants, his code cant run off your stack. > It's been proved many times that non-executable stack adds NO security at all. Every single class of vulnerabilities exploitable with executable stack can be also exploited with non-executable stack. See for example our article (http://www.phrack.org/show.php?p=56&a=5) which shows how to bypass a stack protector even with a non-executable stack. What we're discussing here is an internal structures and data protecting. IMHO the ProPolice (http://www.research.ibm.com/trl/projects/security/ssp/), is the best protection in this kind, even comparing to "two stack" approach. Beside that it's an existing, well tested and wide used (for example OpenBSD uses it by default now). I see no real reason why the major Linux companies are not using it for its products. Best regards, -- Mariusz Woloszyn Internet Security Specialist, GTS - Internet Partners
