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

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Message-ID: <CAEjxPJ4nz=1-eeQtU+V5r_ULvpT9Thh6TB4G=2gu2fivyo6KaA@mail.gmail.com>
Date:   Thu, 11 Jun 2020 12:36:08 -0400
From:   Stephen Smalley <stephen.smalley.work@...il.com>
To:     trix@...hat.com
Cc:     Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>,
        Ondrej Mosnacek <omosnace@...hat.com>, weiyongjun1@...wei.com,
        SElinux list <selinux@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selinux: fix another double free

On Thu, Jun 11, 2020 at 11:58 AM <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 the
> earlier nodes.
>
> Signed-off-by: Tom Rix <trix@...hat.com>

Looks like this was introduced by
60abd3181db29ea81742106cc0ac2e27fd05b418 ("selinux: convert cond_list
to array").

Acked-by: Stephen Smalley <stephen.smalley.work@...il.com>