svn commit: r279335 - in user/dchagin/lemul/sys: compat/linprocfs fs/procfs fs/pseudofs modules/procfs

[Chagin Dmitry]

On Thu, Feb 26, 2015 at 11:03:42PM +0100, Mateusz Guzik wrote:
> On Thu, Feb 26, 2015 at 09:30:41PM +0000, Dmitry Chagin wrote:
> > +int
> > +procfs_dofdlink(PFS_FILL_ARGS)
> > +{
> > +	char *fullpath, *freepath, *endfileno;
> > +	struct filedesc *fdp;
> > +	struct vnode *vp;
> > +	struct file *fp;
> > +	int fileno, error;
> > +
> > +	if (vnode_name == NULL)
> > +		return (ENOENT);
> > +
> > +	fileno = (int)strtol(vnode_name, &endfileno, 10);
> > +	if (fileno == 0 && (vnode_namelen > 1 ||
> > +	    (vnode_namelen == 1 && vnode_name[0] != '0')))
> > +		return (ENOENT);
> > +	if (vnode_namelen != endfileno - vnode_name)
> > +		return (ENOENT);
> > +
> > +	fdp = fdhold(p);
> > +	if (fdp == NULL)
> > +		return (ENOENT);
> > +
> > +	error = fget_unlocked(fdp, fileno, NULL, &fp, NULL);
> > +	if (error != 0)
> > +		goto out;
> > +
> > +	freepath = NULL;
> > +	fullpath = "-";
> > +	vp = fp->f_vnode;
> > +	if (vp != NULL) {
> > +		vref(vp);
> > +		error = vn_fullpath(td, vp, &fullpath, &freepath);
> > +		vrele(vp);
> > +	}
> > +	if (error == 0)
> > +		error = sbuf_printf(sb, "%s", fullpath);
> > +	if (freepath != NULL)
> > +		free(freepath, M_TEMP);
> > +	fdrop(fp, td);
> > +
> > + out:
> > +	fddrop(fdp);
> > +	return (error);
> > +}
> >
> 
> 
> fdhold does not protect file descriptor table, it only makes sure struct
> filedesc itself is not freed.
> 
> Here you need to lock it and inspect fd_refcnt. See e.g.
> kern_proc_filedesc_out.
> 
pfs_readlink does a PHOLD and PRELE around calling fill method, is
this not enought?

> While this guarantees data consistency, is in fact still incorrect since
> the process you are inspecing can exec  setuid in the meantime and thus
> make security checks (if any performed) stale.
> 
> I have an old WIP patch which provides appropriate interfaces to ensure
> stability of the process (no exit, no exec), but this needs additional
> changes. HOpefully i'll have the time to deal with it in March.
ok, give me see the patch, pls.
-- 
Have fun!
chd