netdev - Re: [PATCH bpf-next v10 2/4] bpf: new helper to obtain namespace data from current task New bpf helper bpf_get_current_pidns

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Date:   Fri, 6 Sep 2019 16:46:47 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Carlos Neira <cneirabustos@...il.com>
Cc:     netdev@...r.kernel.org, yhs@...com, ebiederm@...ssion.com,
        brouer@...hat.com, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v10 2/4] bpf: new helper to obtain namespace
 data from  current task New bpf helper bpf_get_current_pidns_info.

On Fri, Sep 06, 2019 at 04:24:35PM +0100, Al Viro wrote:
> > +	tmp = kmalloc(fnamesize, GFP_ATOMIC);
> > +	if (unlikely(!tmp)) {
> > +		__putname(fname);
> > +		ret = -ENOMEM;
> > +		goto clear;
> > +	}
> > +
> > +	tmp->name = (char *)fname;
> > +	fname = tmp;
> > +	len = strlen(pidns_path) + 1;
> > +	memcpy((char *)fname->name, pidns_path, len);
> > +	fname->uptr = NULL;
> > +	fname->aname = NULL;
> > +	fname->refcnt = 1;
> > +
> > +	ret = filename_lookup(AT_FDCWD, fname, 0, &kp, NULL);
> > +	if (ret)
> > +		goto clear;
> 
> Where do I begin?
> 	* getname_kernel() is there for purpose
> 	* so's kern_path(), damnit

Oh, and filename_lookup() *CAN* sleep, obviously.  So that
GFP_ATOMIC above is completely pointless.

> > +
> > +	inode = d_backing_inode(kp.dentry);
> > +	pidns_info->dev = (u32)inode->i_rdev;

Why are plaing with device number, anyway?  And why would it
be anything other than 0?