linux-kernel - Re: [PATCH] sctp: initialize endpoint LSM labels also on the client side

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Message-ID: <CAFqZXNs6xPm-2FU=2mSqMSCivmjP-mDcnGf+FB7tqY1-H=GPgg@mail.gmail.com>
Date:   Thu, 21 Oct 2021 17:52:16 +0200
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     linux-sctp@...r.kernel.org, network dev <netdev@...r.kernel.org>,
        SElinux list <selinux@...r.kernel.org>,
        Linux Security Module list 
        <linux-security-module@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Richard Haines <richard_c_haines@...nternet.com>
Subject: Re: [PATCH] sctp: initialize endpoint LSM labels also on the client side

On Thu, Oct 21, 2021 at 5:38 PM Ondrej Mosnacek <omosnace@...hat.com> wrote:
> The secid* fields in struct sctp_endpoint are used to initialize the
> labels of a peeloff socket created from the given association. Currently
> they are initialized properly when a new association is created on the
> server side (upon receiving an INIT packet), but not on the client side.
>
> As a result, when the client obtains a peeloff socket via
> sctp_peeloff(3) under SELinux, it ends up unlabeled, leading to
> unexpected denials.
>
> Fix this by calling the security_sctp_assoc_request() hook also upon
> receiving a valid INIT-ACK response from the server, so that the
> endpoint labels are properly initialized also on the client side.
>
> Fixes: 2277c7cd75e3 ("sctp: Add LSM hooks")
> Cc: Richard Haines <richard_c_haines@...nternet.com>
> Signed-off-by: Ondrej Mosnacek <omosnace@...hat.com>
> ---
>  include/net/sctp/structs.h | 11 ++++++-----
>  net/sctp/sm_statefuns.c    |  5 +++++
>  2 files changed, 11 insertions(+), 5 deletions(-)

See also the selinux-testsuite [1] patch [2] that verifies this fix
(i.e. the new tests fail without this patch and pass with it). Not
being very familiar with SCTP, I'm not 100% sure if this fix is
correct or complete, so reviews are very much welcome.

[1] https://github.com/SELinuxProject/selinux-testsuite/
[2] https://patchwork.kernel.org/project/selinux/patch/20211021144543.740762-1-omosnace@redhat.com/

>
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 651bba654d77..033a955592dd 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -1356,11 +1356,12 @@ struct sctp_endpoint {
>
>         __u8  strreset_enable;
>
> -       /* Security identifiers from incoming (INIT). These are set by
> -        * security_sctp_assoc_request(). These will only be used by
> -        * SCTP TCP type sockets and peeled off connections as they
> -        * cause a new socket to be generated. security_sctp_sk_clone()
> -        * will then plug these into the new socket.
> +       /* Security identifiers from incoming (INIT/INIT-ACK). These
> +        * are set by security_sctp_assoc_request(). These will only
> +        * be used by SCTP TCP type sockets and peeled off connections
> +        * as they cause a new socket to be generated.
> +        * security_sctp_sk_clone() will then plug these into the new
> +        * socket.
>          */
>
>         u32 secid;
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index 32df65f68c12..cb291c7f5fb7 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -521,6 +521,11 @@ enum sctp_disposition sctp_sf_do_5_1C_ack(struct net *net,
>         if (!sctp_vtag_verify(chunk, asoc))
>                 return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
>
> +       /* Update socket peer label if first association. */
> +       if (security_sctp_assoc_request((struct sctp_endpoint *)ep,
> +                                       chunk->skb))
> +               return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
> +
>         /* 6.10 Bundling
>          * An endpoint MUST NOT bundle INIT, INIT ACK or
>          * SHUTDOWN COMPLETE with any other chunks.
> --
> 2.31.1
>

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