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List:       linux-kernel
Subject:    Re: [PATCH] private mounts
From:       Jamie Lokier <jamie () shareable ! org>
Date:       2005-04-30 23:58:29
Message-ID: 20050430235829.GB11494 () mail ! shareable ! org
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Olivier Galibert wrote:
> > > "mount --bind /proc/self/fd/N mount_point" works, try it.
> > 
> > What do people think about that?
> 
> To me it looks like an atrocious hack that works only because of the
> way the implementation is done and not really by design.

From fs/namespace.c:do_loopback, the function which does bind mounts:

	if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) {

check_mnt() verifies that a mountpoint is in the same namespace as the
current process.  recurse is set for --rbind mounts, but not --bind mounts.

Notice how old_nd.mnt is explicitly _not_ checked for being in the current
namespace when doing --bind?

That says to me that Al thought about this case, and coded for it...

(I'm still not clear why the check_mnt() calls are needed at all, though).

-- Jamie
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