linux-kernel - Re: [patch 7/8] fdmap v2

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Message-ID: <20070609200645.GG4095@ftp.linux.org.uk>
Date:	Sat, 9 Jun 2007 21:06:45 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Kyle Moffett <mrmacman_g4@....com>
Cc:	Ulrich Drepper <drepper@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Theodore Tso <tytso@....edu>,
	Eric Dumazet <dada1@...mosbay.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

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...
-
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