Rich Felker <dalias@xxxxxxxxxx> writes: > On Sat, Jan 10, 2015 at 04:27:23PM -0600, Eric W. Biederman wrote: >> Rich Felker <dalias@xxxxxxxxxx> writes: >> >> > On Sat, Jan 10, 2015 at 04:14:57AM +0000, Al Viro wrote: >> >> >> Except that if your interpreter does stat(2) (or access(2), or getxattr(2), >> >> etc.) before bothering with open(2), you'll get screwed. >> > >> > Yes, but I think that would be very bad interpreter design. >> > stat/getxattr/access/whatever followed by open is always a TOCTOU >> > race. The correct sequence of actions is always open followed by >> > fstat/fgetxattr/... >> >> Sigh. I think everyone who has looked at this has been blind. >> >> If userspace is reasonable all we have to do is fix /proc/self/exe >> for shell scripts to point at the actual script, >> and then pass /proc/self/exe on the shell scripts command line. >> >> At a practical level we have to worry about backwards compability and >> chroot jails. But the existence of a clean implementation with >> /proc/self/exe serves a proof of concept that it would not be too >> difficult. When someone cares enough to implement it. > > Is /proc/self/exe a "magic symlink" that's bound to the inode, or just > a regular symlink? In the latter case it defeats the whole purpose of > using O_EXEC fds and fexecve rather than pathnames. In implementation /proc/self/exe is a named rather than a numbered file descriptor. Essentially when loading an elf executable the file descriptor is duped to the name /proc/self/exe. The implementation otherwise is the same as /proc/self/fd/N. The downside of course is that I expect if we were actually to change /proc/self/exe from to point at the script instead of the shell some piece of software somewhere would come melting down. I am totally not ready to consider that kind of mine field today. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
