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

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Date:   Tue, 16 Jun 2020 20:27:54 -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 v3] selinux: fix another double free

On Mon, Jun 15, 2020 at 4:45 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>
> ---
> 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