linux-kernel - Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks and file bind mounts (try #5)

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Message-ID: <20091123224948.GB5598@shareable.org>
Date:	Mon, 23 Nov 2009 22:49:48 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	pavel@....cz, miklos@...redi.hu, viro@...IV.linux.org.uk
Subject: Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks and file bind mounts (try #5)

Jeff Layton wrote:
> > check_path_accessible seems pretty horrible.   If a process is running
> > inside of a subdirectory it doesn't have permissions to access, say
> > a chroot, /proc/self/fd/XXX becomes completely unusable.
> > 
> 
> Hmm...I have this in there:
> 
> +		/* are we at global root or root of namespace? */
> +		if ((tdentry == root.dentry && vfsmnt == root.mnt) ||
> +		    vfsmnt->mnt_parent == vfsmnt)
> +			break;
> 
> ...In the case of a chroot, wouldn't "current->fs->root" point to the
> root of the process' namespace? Or am I misunderstanding what
> current->fs actually represents?

A process can run inside a subdirectory it doesn't have permissions to
access without that being a chroot.

It can also run inside a subdirectory that isn't accessible from it's
root, if that's how it was started - as well as having other
descriptors pointing to things outside its root.

It can also be passed file descriptors from outside it's root while
it's running.

Really, I think the /proc/PID/fd/N check should restrict the open to
the O_* limitations that were used to open fd N before, and not have
any connection to actual paths at the time of this check.

-- Jamie
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