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

[Al Viro <viro@ftp.linux.org.uk>]

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).
> 
> 
> SCENARIO 1:
> 
> 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...

> SCENARIO 2:
> 
> 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...