linux-kernel - Re: [PATCH 2/4] autofs4 - track uid and gid of last mount requester

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Message-ID: <20080807221242.GA27032@us.ibm.com>
Date:	Thu, 7 Aug 2008 17:12:42 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ian Kent <raven@...maw.net>, autofs@...ux.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	containers@...ts.osdl.org
Subject: Re: [PATCH 2/4] autofs4 - track uid and gid of last mount requester

Quoting Andrew Morton (akpm@...ux-foundation.org):
> On Thu, 07 Aug 2008 19:40:14 +0800
> Ian Kent <raven@...maw.net> wrote:
> 
> > Patch to track the uid and gid of the last process to request a mount
> > for on an autofs dentry.
> 
> pet peeve: changelog should not tell the reader that this is a "patch".
> Because when someone is reading the changelog in the git repository,
> they hopefully already know that.
> 
> > Signed-off-by: Ian Kent <raven@...maw.net>
> > 
> > ---
> > 
> >  fs/autofs4/autofs_i.h |    3 +++
> >  fs/autofs4/inode.c    |    2 ++
> >  fs/autofs4/waitq.c    |   34 ++++++++++++++++++++++++++++++++++
> >  3 files changed, 39 insertions(+), 0 deletions(-)
> > 
> > 
> > diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
> > index ea024d8..fa76d18 100644
> > --- a/fs/autofs4/autofs_i.h
> > +++ b/fs/autofs4/autofs_i.h
> > @@ -63,6 +63,9 @@ struct autofs_info {
> >  	unsigned long last_used;
> >  	atomic_t count;
> >  
> > +	uid_t uid;
> > +	gid_t gid;
> > +
> >  	mode_t	mode;
> >  	size_t	size;
> >  
> > diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
> > index 9ca2d07..9408507 100644
> > --- a/fs/autofs4/inode.c
> > +++ b/fs/autofs4/inode.c
> > @@ -53,6 +53,8 @@ struct autofs_info *autofs4_init_ino(struct autofs_info *ino,
> >  		atomic_set(&ino->count, 0);
> >  	}
> >  
> > +	ino->uid = 0;
> > +	ino->gid = 0;
> >  	ino->mode = mode;
> >  	ino->last_used = jiffies;
> >  
> > diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
> > index 6d87bb1..7c60c0b 100644
> > --- a/fs/autofs4/waitq.c
> > +++ b/fs/autofs4/waitq.c
> > @@ -457,6 +457,40 @@ int autofs4_wait(struct autofs_sb_info *sbi, struct dentry *dentry,
> >  
> >  	status = wq->status;
> >  
> > +	/*
> > +	 * For direct and offset mounts we need to track the requestrer
> 
> typo which I'll fix.
> 
> > +	 * uid and gid in the dentry info struct. This is so it can be
> > +	 * supplied, on request, by the misc device ioctl interface.
> > +	 * This is needed during daemon resatart when reconnecting
> > +	 * to existing, active, autofs mounts. The uid and gid (and
> > +	 * related string values) may be used for macro substitution
> > +	 * in autofs mount maps.
> > +	 */
> > +	if (!status) {
> > +		struct autofs_info *ino;
> > +		struct dentry *de = NULL;
> > +
> > +		/* direct mount or browsable map */
> > +		ino = autofs4_dentry_ino(dentry);
> > +		if (!ino) {
> > +			/* If not lookup actual dentry used */
> > +			de = d_lookup(dentry->d_parent, &dentry->d_name);
> > +			if (de)
> > +				ino = autofs4_dentry_ino(de);
> > +		}
> > +
> > +		/* Set mount requester */
> > +		if (ino) {
> > +			spin_lock(&sbi->fs_lock);
> > +			ino->uid = wq->uid;
> > +			ino->gid = wq->gid;
> > +			spin_unlock(&sbi->fs_lock);
> > +		}
> > +
> > +		if (de)
> > +			dput(de);
> > +	}
> > +
> 
> Please remind me again why autofs's use of current->uid and
> current->gid is not busted in the presence of PID namespaces, where
> these things are no longer system-wide unique?

I actually don't see what the autofs4_waitq->pid is used for.  It's
copied from current into wq->pid at autofs4_wait, and into a packet to
send to userspace (I assume) at autofs4_notify_daemon.

So as long as a daemon can serve multiple pid namespaces (which
doubtless it can), the pid could be confusing (or erroneous) for the
daemon.

If I'm remotely right about how the pid is being used, then the thing to
do would be to 
	1. store the daemon's pid namespace  (would that belong in
	the autofs_sb_info?)
	2. store the task_pid(current) in the waitqueue
	3. retrieve the pid_t for the waiting task in the daemon's
	pid namespace, and put that into the packet at
	autofs4_notify_daemon.

I realize this patch was about the *uids*, but the pids seem more
urgent.

-serge
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