Re: kernel bug in socketpair()

From: David S. Miller (
Date: Wed Jul 23 2003 - 12:00:43 EST

On Wed, 23 Jul 2003 12:56:12 -0400 (EDT)
Glenn Fowler <> wrote:

> the problem is that linux took an implementation shortcut by symlinking
> /dev/fd/N -> /proc/self/fd/N
> and by the time the kernel sees /proc/self/fd/N the "self"-ness is apparently
> lost, and it is forced to do the security checks

None of this is true. If you open /proc/self/fd/N directly the problem
is still there.

> if the /proc fd open code has access to the original /proc/PID/fd/N path
> then it can do dup(atoi(N)) when the PID is the current process without
> affecting security

If we're talking about the current process, there is no use in using
/proc/*/fd/N to open a file descriptor in the first place, you can
simply call open(N,...)

I've personally always viewed /proc/*/fd/N as a way to see who has
various files or sockets open, ie. a debugging tool, not as a generic
way for processes to get access to each other's FDs.

There is an existing mechanism, a portable non-Linux one, that you
can use to do that.

Pass the fd over a UNIX domain socket if you want that, truly.
That works on every system.
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