Messages in this thread | | | From | Kyle Moffett <> | Subject | Re: [patch 7/8] fdmap v2 - implement sys_socket2 | Date | Sat, 9 Jun 2007 15:27:43 -0400 |
| |
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/
| |