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From: Stephen Smalley <stephen.smalley.work@gmail.com>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: casey.schaufler@intel.com, James Morris <jmorris@namei.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	SElinux list <selinux@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	John Johansen <john.johansen@canonical.com>,
	penguin-kernel@i-love.sakura.ne.jp,
	Paul Moore <paul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	linux-audit@redhat.com, netdev@vger.kernel.org
Subject: Re: [PATCH v17 05/23] net: Prepare UDS for security module stacking
Date: Mon, 18 May 2020 13:02:23 -0400
Message-ID: <CAEjxPJ4TExFpm0KJSodLSEG0J+YNYBE4KdKyd=1g-Qs-qgPHpA@mail.gmail.com> (raw)
In-Reply-To: <20200514221142.11857-6-casey@schaufler-ca.com>

On Thu, May 14, 2020 at 7:25 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> Change the data used in UDS SO_PEERSEC processing from a
> secid to a more general struct lsmblob. Update the
> security_socket_getpeersec_dgram() interface to use the
> lsmblob. There is a small amount of scaffolding code
> that will come out when the security_secid_to_secctx()
> code is brought in line with the lsmblob.
>
> The secid field of the unix_skb_parms structure has been
> replaced with a pointer to an lsmblob structure, and the
> lsmblob is allocated as needed. This is similar to how the
> list of passed files is managed. While an lsmblob structure
> will fit in the available space today, there is no guarantee
> that the addition of other data to the unix_skb_parms or
> support for additional security modules wouldn't exceed what
> is available.

I preferred the previous approach (in v15 and earlier) but I see that
this was suggested by Paul.  Lifecycle management of lsmdata seems
rather tenuous. I guess the real question is what does netdev prefer.
Regardless, you need to check for memory allocation failure below if
this approach stands.

> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> cc: netdev@vger.kernel.org
> ---

> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 3385a7a0b231..a5c1a029095d 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -138,17 +138,18 @@ static struct hlist_head *unix_sockets_unbound(void *addr)
>  #ifdef CONFIG_SECURITY_NETWORK
>  static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
>  {
> -       UNIXCB(skb).secid = scm->secid;
> +       UNIXCB(skb).lsmdata = kmemdup(&scm->lsmblob, sizeof(scm->lsmblob),
> +                                     GFP_KERNEL);
>  }

Somewhere you need to check for and handle kmemdup() failure here.

>
>  static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
>  {
> -       scm->secid = UNIXCB(skb).secid;
> +       scm->lsmblob = *(UNIXCB(skb).lsmdata);
>  }

Lest we have a bad day here.

>
>  static inline bool unix_secdata_eq(struct scm_cookie *scm, struct sk_buff *skb)
>  {
> -       return (scm->secid == UNIXCB(skb).secid);
> +       return lsmblob_equal(&scm->lsmblob, UNIXCB(skb).lsmdata);
>  }

Or here.

> diff --git a/net/unix/scm.c b/net/unix/scm.c
> index 8c40f2b32392..3094323935a4 100644
> --- a/net/unix/scm.c
> +++ b/net/unix/scm.c
> @@ -142,6 +142,12 @@ void unix_destruct_scm(struct sk_buff *skb)
>         scm.pid  = UNIXCB(skb).pid;
>         if (UNIXCB(skb).fp)
>                 unix_detach_fds(&scm, skb);
> +#ifdef CONFIG_SECURITY_NETWORK
> +       if (UNIXCB(skb).lsmdata) {
> +               kfree(UNIXCB(skb).lsmdata);
> +               UNIXCB(skb).lsmdata = NULL;
> +       }
> +#endif

Does this suffice to ensure that lsmdata is always freed?  Seems
weakly connected to the allocation.

  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200514221142.11857-1-casey.ref@schaufler-ca.com>
2020-05-14 22:11 ` [PATCH v17 00/23] LSM: Module stacking for AppArmor Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 01/23] LSM: Infrastructure management of the sock security Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 02/23] LSM: Create and manage the lsmblob data structure Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 03/23] LSM: Use lsmblob in security_audit_rule_match Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 04/23] LSM: Use lsmblob in security_kernel_act_as Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 05/23] net: Prepare UDS for security module stacking Casey Schaufler
2020-05-18 17:02     ` Stephen Smalley [this message]
2020-05-14 22:11   ` [PATCH v17 06/23] Use lsmblob in security_secctx_to_secid Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 07/23] LSM: Use lsmblob in security_secid_to_secctx Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 08/23] LSM: Use lsmblob in security_ipc_getsecid Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 09/23] LSM: Use lsmblob in security_task_getsecid Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 10/23] LSM: Use lsmblob in security_inode_getsecid Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 11/23] LSM: Use lsmblob in security_cred_getsecid Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 12/23] IMA: Change internal interfaces to use lsmblobs Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 13/23] LSM: Specify which LSM to display Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 14/23] LSM: Ensure the correct LSM context releaser Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 15/23] LSM: Use lsmcontext in security_secid_to_secctx Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 16/23] LSM: Use lsmcontext in security_inode_getsecctx Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 17/23] LSM: security_secid_to_secctx in netlink netfilter Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 18/23] NET: Store LSM netlabel data in a lsmblob Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 19/23] LSM: Verify LSM display sanity in binder Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 20/23] Audit: Add a new record for multiple subject LSM attributes Casey Schaufler
2020-05-18 18:02     ` Stephen Smalley
2020-05-18 20:42       ` Casey Schaufler
2020-05-18 22:21         ` Paul Moore
2020-05-19  0:16           ` Casey Schaufler
2020-05-19  0:58             ` Casey Schaufler
2020-05-19 15:48             ` Paul Moore
2020-05-14 22:11   ` [PATCH v17 21/23] Audit: Add a new record for multiple object " Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 22/23] LSM: Add /proc attr entry for full LSM context Casey Schaufler
2020-05-14 22:11   ` [PATCH v17 23/23] AppArmor: Remove the exclusive flag Casey Schaufler

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