linux-kernel - Re: [PATCH] afs: proc cells and rootcell are writeable

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Date:	Tue, 28 Jan 2014 09:34:40 -0800
From:	Joe Perches <joe@...ches.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-afs@...ts.infradead.org,
	Pali Rohár <pali.rohar@...il.com>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH] afs: proc cells and rootcell are writeable

On Tue, 2014-01-28 at 13:17 +0100, Geert Uytterhoeven wrote:
> On Tue, Jan 28, 2014 at 1:04 PM, Ingo Molnar <mingo@...nel.org> wrote:
> > * Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> >> On Sun, Jan 26, 2014 at 9:25 PM, Ingo Molnar <mingo@...nel.org> wrote:
> >> > * Ingo Molnar <mingo@...nel.org> wrote:
> >> >> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> >> >> > On Sun, Jan 26, 2014 at 4:27 AM, David Howells <dhowells@...hat.com> wrote:
> >> >> > > -       p = proc_create("cells", 0, proc_afs, &afs_proc_cells_fops);
> >> >> > > +       p = proc_create("cells", S_IFREG | S_IRUGO | S_IWUSR, proc_afs, &afs_proc_cells_fops);
> >> >> > > -       p = proc_create("rootcell", 0, proc_afs, &afs_proc_rootcell_fops);
> >> >> > > +       p = proc_create("rootcell", S_IFREG | S_IRUGO | S_IWUSR, proc_afs, &afs_proc_rootcell_fops);
> >> >> >
> >> >> > So the S_IFREG isn't necessary.
> >> >> >
> >> >> > And quite frankly, I personally think S_IRUGO | S_IWUSR is _less_
> >> >> > readable than 0644. It's damn hard to parse those random letter
> >> >> > combinations, and at least I have to really think about it, in a way
> >> >> > that the octal representation does *not* make me go "I have to think
> >> >> > about that".
> >> >> >
> >> >> > So my personal preference would be to just see that simple 0644 in
> >> >> > proc_create. Hmm?

I don't have an issue with octal uses here either.

I think just as clear if not clearer than defines like

#define {whatever_}rwxrwxrwx	0777
#define {whatever_}rw_r__r__	0644
#define {whatever_}r________	0400

etc...

> >> Only a limited number of combinations is in active use, right?
> > Correct - and in fact that kind of limitation is also a security
> > feature: using patterns _outside_ of the typical, already defined
> > group of permission patterns would in itself be a 'is that really
> > justified?' red flag during review.
> 
> Then Joe (CCed :-) can write a checkpatch rule to flag all new users of the
> I_S[RWX}* flags..,

Flagging all "odd" uses of octal too?

Perhaps a checkpatch rule might look something like:
---
 scripts/checkpatch.pl | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 0ea2a1e..bf278e0 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -328,6 +328,12 @@ our $typeTypedefs = qr{(?x:
 	atomic_t
 )};
 
+our $permissions = qr{(?x:
+	S_I[RWX](?:USR|GRP|OTH)|
+	S_IRWX[UGO]|
+	S_I(?:RWX|ALL|R|W|X)UGO
+)};
+
 our $logFunctions = qr{(?x:
 	printk(?:_ratelimited|_once|)|
 	(?:[a-z0-9]+_){1,2}(?:printk|emerg|alert|crit|err|warning|warn|notice|info|debug|dbg|vdbg|devel|cont|WARN)(?:_ratelimited|_once|)|
@@ -4457,6 +4463,15 @@ sub process {
 			WARN("EXPORTED_WORLD_WRITABLE",
 			     "Exporting world writable files is usually an error. Consider more restrictive permissions.\n" . $herecurr);
 		}
+
+# check for uses of permissions S_I<FOO> defines
+		if ($line =~ /\b($permissions)\b/) {
+			my $perm = $1;
+			my $msg_type = \&WARN;
+			$msg_type = \&CHK if ($file);
+			&{$msg_type}("PERMISSIONS",
+				     "Use of $perm is not preferred.\n" . $herecurr);
+		}
 	}
 
 	# If we have no input at all, then there is nothing to report on


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