On Mon, Jan 12, 2015 at 11:33:49AM +0000, David Drysdale wrote: > On Sat, Jan 10, 2015 at 1:33 AM, Rich Felker <dalias@xxxxxxxxxx> wrote: > > On Fri, Jan 09, 2015 at 07:17:41PM -0600, Eric W. Biederman wrote: > >> Rich Felker <dalias@xxxxxxxxxx> writes: > >> > >> > I'm not proposing code because I'm a libc developer not a kernel > >> > developer. I know what's needed for userspace to provide a conforming > >> > fexecve to applications, not how to implement that on the kernel side, > >> > although I'm trying to provide constructive ideas. The hostility is > >> > really not necessary. > >> > >> Conforming to what? > >> > >> The open group fexecve says nothing about requiring a file descriptor > >> passed to fexecve to have O_CLOEXEC. > > > > It doesn't require it but it allows it, and in multithreaded programs > > that might run child processes (or library code that might be used in > > such situations), O_CLOEXEC is mandatory everywhere to avoid fd leaks. > > As a naive idea related to Andy's suggestion elsewhere, could you > just have an environment convention for fexecve-ing scripts? That > would reduce FD leaks without any need for kernel involvement/changes. > > For example, set _FEXECVED_VIA_FD=4 but don't set > O_CLOEXEC before fexecve, and the interpreter reads then > closes that FD. Or just get the interpreter to spot scripts named > "/dev/fd/%d" and read-then-close the FD that way, cf. Eric's suggestion > at https://lkml.org/lkml/2014/10/22/652. No. Any omission of O_CLOEXEC even momentarily is a potentially dangerous fd leak. This is the case whenever the process is multithreaded and it's possible that other threads might fork and exec. Think of the case of a privileged daemon re-execing itself (e.g. to switch to an updated version) while there are potentially other threads spawning non-privileged processes. Rich -- 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
