linux-kernel - Re: [PATCH 1/3] selinux: consistently clear cond

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Date:   Wed, 2 Feb 2022 12:15:07 +0100
From:   Vratislav Bendel <vbendel@...hat.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     stephen.smalley.work@...il.com, eparis@...isplace.org,
        Ondrej Mosnacek <omosnace@...hat.com>, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] selinux: consistently clear cond_list on error paths

On Tue, Feb 1, 2022 at 9:10 PM Paul Moore <paul@...l-moore.com> wrote:
>
> On Tue, Feb 1, 2022 at 12:38 PM Paul Moore <paul@...l-moore.com> wrote:
> > On Fri, Jan 28, 2022 at 3:29 PM <vbendel@...hat.com> wrote:
> > > From: Vratislav Bendel <vbendel@...hat.com>
> > >
> > > Currently there are two users of policydb->cond_list: cond_read_list()
> > > and duplicate_policydb_cond_list(). On their error path one clears
> > > ->cond_list to NULL, but the other doesn't.
> > > Make the behavior consistent by resetting ->cond_list to NULL in
> > > cond_list_destroy(), which is called by both on the error path.
> >
> > It's also important to see if there are any callers of
> > cond_list_destroy() which incorrectly might be making use of
> > policydb::cond_list after it has been freed; thankfully that does not
> > appear to be the case in any of the call paths I looked at just now.
> > As this is more a a style/Right-Thing-To-Do patch and not an immediate
> > bugfix I'm going to go and merge this into selinux/next.
>
> After looking at patches 2/3 and 3/3, ignore the last sentence above
> and see my comments below :)
>
> > Thanks Vratislav.
> >
> > > Signed-off-by: Vratislav Bendel <vbendel@...hat.com>
> > > ---
> > >  security/selinux/ss/conditional.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
> > > index 2ec6e5cd25d9..1d0e5f326b62 100644
> > > --- a/security/selinux/ss/conditional.c
> > > +++ b/security/selinux/ss/conditional.c
> > > @@ -152,6 +152,7 @@ static void cond_list_destroy(struct policydb *p)
> > >         for (i = 0; i < p->cond_list_len; i++)
> > >                 cond_node_destroy(&p->cond_list[i]);
> > >         kfree(p->cond_list);
> > > +       p->cond_list = NULL;
>
> While patch 1/3 may not be a candidate for selinux/stable-5.17 by
> itself, patch 2/3 definitely qualifies.  Considering that both patches
> are small, easily understood, and the likelihood of a merge conflict
> between the two is high, why don't you squash 1/3 and 2/3 together so
> we can submit this for selinux/stable-5.17?  In addition, put the two
> lines which reset cond_list and cond_list_len together in v2, it's
> cleaner that way, example below.  If you don't have time to do that
> let me know and I can squash them together and move the
> "p->cond_list_len = 0" line (don't worry, I'll preserve your
> name/email as the patch author).

I was also wondering about the possible conflict for submission
into stable. I see no problem with squashing 1/3 and 2/3 together.
I'll send the v2, as per your suggestions. :)

Thank you and have a nice day!

>
>   static void cond_list_destroy(...)
>   {
>
>     /* ... */
>
>     kfree(p->cond_list);
>     p->cond_list = NULL;
>     p->cond_list_len = 0;
>   }
>
> > >  }
> > >
> > >  void cond_policydb_destroy(struct policydb *p)
> > > @@ -441,7 +442,6 @@ int cond_read_list(struct policydb *p, void *fp)
> > >         return 0;
> > >  err:
> > >         cond_list_destroy(p);
> > > -       p->cond_list = NULL;
> > >         return rc;
> > >  }
>
> --
> paul-moore.com
>