Linux-Security-Module Archive on lore.kernel.org
 help / color / Atom feed
From: Paul Moore <paul@paul-moore.com>
To: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: David Howells <dhowells@redhat.com>,
	keyrings@vger.kernel.org, SElinux list <selinux@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms
Date: Mon, 27 Apr 2020 18:17:46 -0400
Message-ID: <CAHC9VhTSuWLheaQDXwEyELGXEJOAXoFr2--FYhiviQbDHQKhkw@mail.gmail.com> (raw)
In-Reply-To: <CAEjxPJ4S0wpAtXoD1f-54qrriRC8y_hj9T5-vKOGDmf1XhOLrQ@mail.gmail.com>

On Mon, Apr 27, 2020 at 1:02 PM Stephen Smalley
<stephen.smalley.work@gmail.com> wrote:
> On Mon, Apr 27, 2020 at 10:13 AM David Howells <dhowells@redhat.com> wrote:

...

> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 0b4e32161b77..6087955b49d8 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -6539,20 +6539,38 @@ static void selinux_key_free(struct key *k)
> >         kfree(ksec);
> >  }
> >
> > +static unsigned int selinux_keyperm_to_av(unsigned int need_perm)
> > +{
> > +       switch (need_perm) {
> > +       case KEY_NEED_VIEW:     return KEY__VIEW;
> > +       case KEY_NEED_READ:     return KEY__READ;
> > +       case KEY_NEED_WRITE:    return KEY__WRITE;
> > +       case KEY_NEED_SEARCH:   return KEY__SEARCH;
> > +       case KEY_NEED_LINK:     return KEY__LINK;
> > +       case KEY_NEED_SETATTR:  return KEY__SETATTR;
> > +       default:
>
> Possibly WARN() or BUG() here?  Or BUILD_BUG_ON(KEY_NEED_ALL != 0x3f)
> to force an update here
> whenever a new key permission is defined?

My vote is for a build time check via BUILD_BUG_ON() or similar
mechanism.  It's worked really well in other places, I'm thinking
specifically of the SELinux netlink mapping.

> > +               return 0;
> > +       }
> > +}
> > +
> >  static int selinux_key_permission(key_ref_t key_ref,
> >                                   const struct cred *cred,
> > -                                 unsigned perm)
> > +                                 unsigned need_perm)
> >  {
> >         struct key *key;
> >         struct key_security_struct *ksec;
> > +       unsigned int perm;
> >         u32 sid;
> >
> >         /* if no specific permissions are requested, we skip the
> >            permission check. No serious, additional covert channels
> >            appear to be created. */
> > -       if (perm == 0)
> > +       if (need_perm == 0)
> >                 return 0;
> >
> > +       perm = selinux_keyperm_to_av(need_perm);
> > +       if (perm == 0)
> > +               return -EACCES;
>
> We should log or audit some kind of message here, whether via WARN(),
> audit_log(), or something, to avoid silent denials.

Assuming we add a build time check (see above), I think a WARN here is okay.

-- 
paul moore
www.paul-moore.com

  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-17 15:48 Problem with 9ba09998baa9 ("selinux: Implement the watch_key security hook") in linux-next Paul Moore
2020-04-17 16:32 ` Richard Haines
2020-04-17 16:59   ` Paul Moore
2020-04-21 12:29 ` David Howells
2020-04-22 19:20   ` Paul Moore
2020-04-22 21:09     ` Paul Moore
2020-04-24 23:43   ` David Howells
2020-04-26 20:53     ` Paul Moore
2020-04-27 14:12     ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms David Howells
2020-04-27 14:36       ` Stephen Smalley
2020-04-27 15:24         ` Paul Moore
2020-04-27 17:02       ` Stephen Smalley
2020-04-27 22:17         ` Paul Moore [this message]
2020-04-28 12:54 ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms [v2] David Howells
2020-04-28 14:32   ` Stephen Smalley
2020-04-28 15:57   ` David Howells
2020-04-28 16:19     ` Stephen Smalley
2020-05-01 16:37       ` Paul Moore
2020-05-12 22:33       ` [PATCH] keys: Make the KEY_NEED_* perms an enum rather than a mask David Howells
2020-05-13  1:04         ` Paul Moore
2020-05-13 12:58         ` Stephen Smalley
2020-05-13 15:25         ` Casey Schaufler
2020-05-13 23:13         ` David Howells
2020-05-14 12:08           ` Stephen Smalley
2020-05-14 14:45             ` Stephen Smalley
2020-05-13 23:16         ` David Howells
2020-05-13 23:25         ` David Howells
2020-05-14 11:00         ` Jarkko Sakkinen
2020-05-14 16:58         ` [PATCH] keys: Move permissions checking decisions into the checking code David Howells
2020-05-14 17:06           ` Casey Schaufler
2020-05-15 15:06           ` Stephen Smalley
2020-05-15 16:45           ` David Howells
2020-05-15 18:55             ` Stephen Smalley
2020-05-15 19:10               ` Casey Schaufler
2020-05-15 22:27             ` David Howells

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAHC9VhTSuWLheaQDXwEyELGXEJOAXoFr2--FYhiviQbDHQKhkw@mail.gmail.com \
    --to=paul@paul-moore.com \
    --cc=dhowells@redhat.com \
    --cc=keyrings@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=selinux@vger.kernel.org \
    --cc=stephen.smalley.work@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Security-Module Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-security-module/0 linux-security-module/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-security-module linux-security-module/ https://lore.kernel.org/linux-security-module \
		linux-security-module@vger.kernel.org
	public-inbox-index linux-security-module

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-security-module


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git