lkml.org 
[lkml]   [2007]   [Jun]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch 7/8] fdmap v2 - implement sys_socket2
Date
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 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!!!


SCENARIO 2:

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

Here we were trying to safely call into code which reads from stdin
and shouldn't be given privileged data, but the syslet makes the
common paradigm 'close(0); open("/dev/null");' horribly insecure.

If you extend all the FD syscalls to all take a "flags" parameter and
add the appropriate flags, then you can pass O_CLOEXEC|O_RANDFD to
whatever syscall you are using and both problems vanish.

Cheers,
Kyle Moffett

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-09 21:31    [W:0.263 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site