On Tue, Oct 27, 2009 at 12:29:09AM +0300, Dan Yefimov wrote: > and testing them. Remember the scenario from the original mail and try > finding a window, during which creating a hardlink would still work thus > evading directory permissions check.
The main thing this does is allow a hardlink-like attack to work across mountpoints afaics. Instead of making hardlink you run something that keeps an fd open to the file. That said, I don't see how this is a vuln in /proc. Can you not have your little program seek back to the beginning and re-read the file in order to track changes? You can't actually use /proc/*/fd to gain access to files opened by processes you do not own. Only ones you do (at least in a mainline kernel) which is fair enough. This means that you can't have user a open a file owned by user b and then let user c have access to it via /proc/$pid/fd. Or am I misreading/misunderstanding something? I've not tested all of the above (no time). Just going off remembered experience. -- "A search of his car uncovered pornography, a homemade sex aid, women's stockings and a Jack Russell terrier." - http://www.news.com.au/story/0%2C27574%2C24675808-421%2C00.html