linux-kernel - Re: [PATCH v2 1/1] selinux: fix another double free

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Date:   Thu, 11 Jun 2020 18:30:38 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     trix@...hat.com
Cc:     Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Ondrej Mosnacek <omosnace@...hat.com>, weiyongjun1@...wei.com,
        selinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] selinux: fix another double free

On Thu, Jun 11, 2020 at 4:48 PM <trix@...hat.com> wrote:
> From: Tom Rix <trix@...hat.com>
>
> Clang static analysis reports this double free error
>
> security/selinux/ss/conditional.c:139:2: warning: Attempt to free released memory [unix.Malloc]
>         kfree(node->expr.nodes);
>         ^~~~~~~~~~~~~~~~~~~~~~~
>
> When cond_read_node fails, it calls cond_node_destroy which frees the
> node but does not poison the entry in the node list.  So when it
> returns to its caller cond_read_list, cond_read_list deletes the
> partial list.  The latest entry in the list will be deleted twice.
>
> So instead of freeing the node in cond_read_node, let list freeing in
> code_read_list handle the freeing the problem node along with all of the
> earlier nodes.
>
> Because cond_read_node no longer does any error handling, the goto's
> the error case are redundant.  Instead just return the error code.
>
> Fixes a problem was introduced by commit
>
>   selinux: convert cond_list to array
>
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  security/selinux/ss/conditional.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)

Hi Tom,

Thanks for the patch!  A few more notes, in no particular order:

* There is no need to send a cover letter for just a single patch.
Typically cover letters are reserved for large patchsets that require
some additional explanation and/or instructions beyond the individual
commit descriptions.

* Thank you for including a changelog with your patch updates, but it
would be helpful if you included them in the patch by using a "---"
delimiter in the commit description after your signoff but before the
diffstat.  Here is a recent example:
-> https://lore.kernel.org/selinux/20200611135303.19538-3-cgzones@googlemail.com

* When referencing a patch which you are "fixing", the proper syntax
is 'Fixes: <12char_commitID> ("<subject_line")'.  Look at commit
46619b44e431 in Linus' tree to see an example.

If you have any questions, let us know.

> diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
> index da94a1b4bfda..d0d6668709f0 100644
> --- a/security/selinux/ss/conditional.c
> +++ b/security/selinux/ss/conditional.c
> @@ -392,26 +392,21 @@ static int cond_read_node(struct policydb *p, struct cond_node *node, void *fp)
>
>                 rc = next_entry(buf, fp, sizeof(u32) * 2);
>                 if (rc)
> -                       goto err;
> +                       return rc;
>
>                 expr->expr_type = le32_to_cpu(buf[0]);
>                 expr->bool = le32_to_cpu(buf[1]);
>
>                 if (!expr_node_isvalid(p, expr)) {
>                         rc = -EINVAL;
> -                       goto err;
> +                       return rc;
>                 }
>         }
>
>         rc = cond_read_av_list(p, fp, &node->true_list, NULL);
>         if (rc)
> -               goto err;
> +               return rc;
>         rc = cond_read_av_list(p, fp, &node->false_list, &node->true_list);
> -       if (rc)
> -               goto err;
> -       return 0;
> -err:
> -       cond_node_destroy(node);
>         return rc;
>  }
>
> --
> 2.18.1

--
paul moore
www.paul-moore.com