[v19,19/23] LSM: Verify LSM display sanity in binder
diff mbox series

Message ID 20200724203226.16374-20-casey@schaufler-ca.com
State New
Headers show
Series
  • LSM: Module stacking for AppArmor
Related show

Commit Message

Casey Schaufler July 24, 2020, 8:32 p.m. UTC
Verify that the tasks on the ends of a binder transaction
use the same "display" security module. This prevents confusion
of security "contexts".

Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 security/security.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

Comments

John Johansen July 30, 2020, 8:40 a.m. UTC | #1
On 7/24/20 1:32 PM, Casey Schaufler wrote:
> Verify that the tasks on the ends of a binder transaction
> use the same "display" security module. This prevents confusion
> of security "contexts".
> 

Reviewed-by: John Johansen <john.johansen@canonical.com>

> Reviewed-by: Kees Cook <keescook@chromium.org>
> Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
>  security/security.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/security/security.c b/security/security.c
> index ddbaf2073b02..95b48721fb17 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -788,9 +788,38 @@ int security_binder_set_context_mgr(struct task_struct *mgr)
>  	return call_int_hook(binder_set_context_mgr, 0, mgr);
>  }
>  
> +/**
> + * security_binder_transaction - Binder driver transaction check
> + * @from: source of the transaction
> + * @to: destination of the transaction
> + *
> + * Verify that the tasks have the same LSM "display", then
> + * call the security module hooks.
> + *
> + * Returns -EINVAL if the displays don't match, or the
> + * result of the security module checks.
> + */
>  int security_binder_transaction(struct task_struct *from,
>  				struct task_struct *to)
>  {
> +	int from_display = lsm_task_display(from);
> +	int to_display = lsm_task_display(to);
> +
> +	/*
> +	 * If the display is LSMBLOB_INVALID the first module that has
> +	 * an entry is used. This will be in the 0 slot.
> +	 *
> +	 * This is currently only required if the server has requested
> +	 * peer contexts, but it would be unwieldly to have too much of
> +	 * the binder driver detail here.
> +	 */
> +	if (from_display == LSMBLOB_INVALID)
> +		from_display = 0;
> +	if (to_display == LSMBLOB_INVALID)
> +		to_display = 0;
> +	if (from_display != to_display)
> +		return -EINVAL;
> +
>  	return call_int_hook(binder_transaction, 0, from, to);
>  }
>  
>

Patch
diff mbox series

diff --git a/security/security.c b/security/security.c
index ddbaf2073b02..95b48721fb17 100644
--- a/security/security.c
+++ b/security/security.c
@@ -788,9 +788,38 @@  int security_binder_set_context_mgr(struct task_struct *mgr)
 	return call_int_hook(binder_set_context_mgr, 0, mgr);
 }
 
+/**
+ * security_binder_transaction - Binder driver transaction check
+ * @from: source of the transaction
+ * @to: destination of the transaction
+ *
+ * Verify that the tasks have the same LSM "display", then
+ * call the security module hooks.
+ *
+ * Returns -EINVAL if the displays don't match, or the
+ * result of the security module checks.
+ */
 int security_binder_transaction(struct task_struct *from,
 				struct task_struct *to)
 {
+	int from_display = lsm_task_display(from);
+	int to_display = lsm_task_display(to);
+
+	/*
+	 * If the display is LSMBLOB_INVALID the first module that has
+	 * an entry is used. This will be in the 0 slot.
+	 *
+	 * This is currently only required if the server has requested
+	 * peer contexts, but it would be unwieldly to have too much of
+	 * the binder driver detail here.
+	 */
+	if (from_display == LSMBLOB_INVALID)
+		from_display = 0;
+	if (to_display == LSMBLOB_INVALID)
+		to_display = 0;
+	if (from_display != to_display)
+		return -EINVAL;
+
 	return call_int_hook(binder_transaction, 0, from, to);
 }