linux-kernel - Re: [PATCH 2/3] Make static usermode helper binaries constant

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Message-ID: <1484669260.2886.8.camel@poochiereds.net>
Date:   Tue, 17 Jan 2017 11:07:40 -0500
From:   Jeff Layton <jlayton@...chiereds.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Thomas Sailer <t.sailer@...mni.ethz.ch>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Johan Hovold <johan@...nel.org>, Alex Elder <elder@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        David Howells <dhowells@...hat.com>, NeilBrown <neilb@...e.com>
Subject: Re: [PATCH 2/3] Make static usermode helper binaries constant

On Tue, 2017-01-17 at 16:56 +0100, Greg KH wrote:
> On Tue, Jan 17, 2017 at 10:45:45AM -0500, Jeff Layton wrote:
> > On Mon, 2017-01-16 at 17:50 +0100, Greg KH wrote:
> > > From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > 
> > > There are a number of usermode helper binaries that are "hard coded" in
> > > the kernel today, so mark them as "const" to make it harder for someone
> > > to change where the variables point to.
> > > 
> > > Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > > Cc: Thomas Sailer <t.sailer@...mni.ethz.ch>
> > > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
> > > Cc: Johan Hovold <johan@...nel.org>
> > > Cc: Alex Elder <elder@...nel.org>
> > > Cc: "J. Bruce Fields" <bfields@...ldses.org>
> > > Cc: Jeff Layton <jlayton@...chiereds.net>
> > > Cc: David Howells <dhowells@...hat.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> 
> 
> > > --- a/fs/nfsd/nfs4layouts.c
> > > +++ b/fs/nfsd/nfs4layouts.c
> > > @@ -613,6 +613,7 @@ nfsd4_cb_layout_fail(struct nfs4_layout_stateid *ls)
> > >  {
> > >  	struct nfs4_client *clp = ls->ls_stid.sc_client;
> > >  	char addr_str[INET6_ADDRSTRLEN];
> > > +	static char const nfsd_recall_failed[] = "/sbin/nfsd-recall-failed";
> > >  	static char *envp[] = {
> > >  		"HOME=/",
> > >  		"TERM=linux",
> > > @@ -628,12 +629,13 @@ nfsd4_cb_layout_fail(struct nfs4_layout_stateid *ls)
> > >  		"nfsd: client %s failed to respond to layout recall. "
> > >  		"  Fencing..\n", addr_str);
> > >  
> > > -	argv[0] = "/sbin/nfsd-recall-failed";
> > > +	argv[0] = (char *)nfsd_recall_failed;
> > >  	argv[1] = addr_str;
> > >  	argv[2] = ls->ls_file->f_path.mnt->mnt_sb->s_id;
> > >  	argv[3] = NULL;
> > >  
> > > -	error = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
> > > +	error = call_usermodehelper(nfsd_recall_failed, argv, envp,
> > > +				    UMH_WAIT_PROC);
> > >  	if (error) {
> > >  		printk(KERN_ERR "nfsd: fence failed for client %s: %d!\n",
> > >  			addr_str, error);
> > 
> > Do we need a similar fix in nfsd4_umh_cltrack_upcall?
> 
> Not that I can tell, as the call_usermodehelper() binary it calls is
> dynamically created (it's not a static string).  Unless I'm misreading
> the code?
> 

It's a module_param_string:

static char cltrack_prog[PATH_MAX] = "/sbin/nfsdcltrack";
module_param_string(cltrack_prog, cltrack_prog, sizeof(cltrack_prog),
                        S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(cltrack_prog, "Path to the nfsdcltrack upcall
program");

Maybe we should consider deprecating that module parameter and make it
const as well? I added it when I first developed that code, but I doubt
anyone legitimately sets it.

-- 
Jeff Layton <jlayton@...chiereds.net>