linux-kernel - Re: [RFC PATCH v4 1/4] KEYS: special dot prefixed keyring name bug fix

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Date:	Fri, 30 May 2014 13:58:24 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:	linux-security-module <linux-security-module@...r.kernel.org>,
	Dmitry Kasatkin <d.kasatkin@...sung.com>,
	David Howells <dhowells@...hat.com>,
	Josh Boyer <jwboyer@...hat.com>,
	keyrings <keyrings@...ux-nfs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v4 1/4] KEYS: special dot prefixed keyring name bug
 fix

On Fri, 2014-05-30 at 18:58 +0300, Dmitry Kasatkin wrote: 
> On 28 May 2014 18:09, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> > Dot prefixed keyring names are supposed to be reserved for the
> > kernel, but add_key() calls key_get_type_from_user(), which
> > incorrectly verifies the 'type' field, not the 'description' field.
> > This patch verifies the 'description' field isn't dot prefixed,
> > when creating a new keyring, and removes the dot prefix test in
> > key_get_type_from_user().
> >
> > Reported-by: Dmitry Kasatkin <d.kasatkin@...sung.com>
> > Cc: David Howells <dhowells@...hat.com>
> > Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> > ---
> >  security/keys/keyctl.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
> > index cd5bd0c..9e9a762 100644
> > --- a/security/keys/keyctl.c
> > +++ b/security/keys/keyctl.c
> > @@ -37,8 +37,6 @@ static int key_get_type_from_user(char *type,
> >                 return ret;
> >         if (ret == 0 || ret >= len)
> >                 return -EINVAL;
> > -       if (type[0] == '.')
> > -               return -EPERM;
> >         type[len - 1] = '\0';
> >         return 0;
> >  }
> > @@ -87,6 +85,10 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
> >                         kfree(description);
> >                         description = NULL;
> >                 }
> > +               if (description[0] == '.') {
> > +                       ret = -EPERM;
> > +                       goto error2;
> > +               }
> 
> 1. 3 lines above "discription = NULL" will cause kernel oops...
> It happens when using empty description... like:
> 
> cat x509_ima.der | keyctl padd asymmetric "" keyid

Right, that should be 'else if'. 

> 2. It prevents adding trusted keys to ".ima" from user space...
> This is NOT what we want... right?

It prevents creating a dot prefixed keyring.

Mimi

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