Re: [patch 7/8] fdmap v2 - implement sys_socket2

From: Al Viro
Date: Sat Jun 09 2007 - 16:07:13 EST

On Sat, Jun 09, 2007 at 03:27:43PM -0400, Kyle Moffett wrote:
> On Jun 09, 2007, at 13:24:29, Al Viro wrote:
> >On Sat, Jun 09, 2007 at 10:08:59AM -0700, Ulrich Drepper wrote:
> >>- - there are two interface to use: open + fcntl. This is racy.
> >>And don't tell me this doesn't matter.
> >Racy with respect to what? Return-to-libc exploits from another
> >thread?
> How about racy with respect to normal open

How the hell can it be racy wrt normal open()? F_DUPFD is not dup2(),
it's non-overriding.

> or fork+exec from another
> thread? Specifically there are cases where libc or other libraries
> want to create a backend thread dealing with file descriptors in
> response to the program's straightforward calls into that library
> (Examples include using syslets or event-based polling threads).
> Program Thread: Library Thread:
> fd = socket(AF_*, SOCK_*, 0);
> fork();
> int x = FD_CLOEXEC;
> fcntl(fd, F_SETFD, &x);
> New Process:
> setgroups(...);
> seteuid(...);
> exec(....);
> Whoops!!! Suddenly the user process executed by the (theoretically)
> single-threaded program got a handle to a netlink socket affecting
> some system resource!!!

Give me a break. fork(3) is nowhere near plain fork(2); read the nptl
code for details. Getting a low-overhead exclusion into that scheme is not
a rocket science. And lose the bangs, please...

> Program Thread: Async libc getpwent()-cache syslet
> close(0);
> fd = open("/etc/shadow");
> open("/dev/null");
> code_which_insecurely_reads_from_stdin();

>From what, again? Use of stdio after that is deep in nasal demon land...
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