Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200615204548.9230-1-trix@redhat.com>
In-Reply-To: <20200615204548.9230-1-trix@redhat.com>
From:   Paul Moore <paul@paul-moore.com>
Date:   Tue, 16 Jun 2020 20:27:54 -0400
Message-ID: <CAHC9VhQeo6_mie65AH5bzV9484UWsPQA6kz67ZR7_WSfBQ-3cQ@mail.gmail.com>
Subject: Re: [PATCH v3] selinux: fix another double free
To:     trix@redhat.com
Cc:     Stephen Smalley <stephen.smalley.work@gmail.com>,
        Eric Paris <eparis@parisplace.org>,
        Ondrej Mosnacek <omosnace@redhat.com>, weiyongjun1@huawei.com,
        selinux@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Jun 15, 2020 at 4:45 PM <trix@redhat.com> wrote:
> From: Tom Rix <trix@redhat.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: 60abd3181db2 ("selinux: convert cond_list to array")
>
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
> v3: simplify returns
>
>  security/selinux/ss/conditional.c | 18 +++++-------------
>  1 file changed, 5 insertions(+), 13 deletions(-)

Merged into selinux/stable-5.8 with a better subject line.  Thanks for
catching this and submitting the fix.  Assuming everything goes well
I'll send this up to Linus later this week.

It might be nice to do a follow-up patch for selinux/next which folds
cond_node_destroy() into cond_list_destroy() as there is no longer a
need for that code to be in a separate function.

-- 
paul moore
www.paul-moore.com