linux-kernel - Re: [PATCH 0/3] selinux: Fix and clean policydb->cond

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Message-ID: <CAFqZXNvG+-8FcEgcbKxmUeMznVp6NBAoPctN4EHCc3i-DZA8jQ@mail.gmail.com>
Date:   Mon, 31 Jan 2022 13:06:43 +0100
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     vbendel@...hat.com
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        SElinux list <selinux@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] selinux: Fix and clean policydb->cond_list error paths

On Fri, Jan 28, 2022 at 9:29 PM <vbendel@...hat.com> wrote:
> There are two users of policydb->cond_list: cond_read_list()
> and duplicate_policydb_cond_list(). If any of them gets an error,
> usually an -ENOMEM, the error-path-cleanup *_destroy() functions
> get called twice: firstly from these two and secondly from
> the caller functions' error paths.
>
> In case such -ENOMEM happens while assigning cond_node data, i.e.
> while ->cond_list_len is already non-zero, it leads to inappropriate
> dereferencing of policydb->cond_list[] data in the second called
> cond_list_destroy() from the caller functions' error paths, resulting
> with:
> - NULL pointer deref from cond_read_list();
> - use-after-free + double-free from duplicate_policydb_cond_list().
> (the cond_read_list() manages to set ->cond_list to NULL)
>
> Patch 1/3 simply makes the error behavior consistent by always setting
> ->cond_list to NULL.
>
> Patch 2/3 fixes the actual bug by resetting ->cond_list_len to 0,
> so any subsequent cond_list_destroy() calls would become noop.
>
> Patch 3/3 cleans up the duplicate *_destroy calls on these error paths,
> albeit it's a bit questionable and I'm looking for feedback on it:
> - on one hand the idea is that the caller functions call the *_destroy()
> bits anyway, hence removing duplicate efforts (which also fixes the bug,
> but I'd still prefer to apply patches 1 and 2 regardless);
> - on the other hand it's appropriate and more bug-proof for a function
> to clean everything it allocated on error.
> Hence I'm looking forward to seeing what approach the upstream would find
> more appropriate.
>
> Signed-off-by: Vratislav Bendel <vbendel@...hat.com>

For the series (with or without the last patch):
Reviewed-by: Ondrej Mosnacek <omosnace@...hat.com>

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