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. By the way, FreeBSD has a fexecve(2) syscall that behaves in the same way as the current Linux code for an O_CLOEXEC script -- the interpreter fails to open "/dev/fd/6" as it's gone. Do you know if there are any other OSes that already do something more sophisticated for this case? -- 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
