linux-kernel - Re: [PATCH v3] selinux: fix another double free

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Message-ID: <CAFqZXNsK8HEUVSEr9ENGMtx6Q2=f6hMYO03J5wgSMM2KesNMGg@mail.gmail.com>
Date:   Tue, 16 Jun 2020 10:13:08 +0200
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Tom Rix <trix@...hat.com>
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        SElinux list <selinux@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] selinux: fix another double free

On Mon, Jun 15, 2020 at 10:46 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: 60abd3181db2 ("selinux: convert cond_list to array")
>
> Signed-off-by: Tom Rix <trix@...hat.com>

Reviewed-by: Ondrej Mosnacek <omosnace@...hat.com>

Thanks!

-- 
Ondrej Mosnacek
Software Engineer, Platform Security - SELinux kernel
Red Hat, Inc.