Commit f4384b3e authored by Rijo Thomas's avatar Rijo Thomas Committed by Jens Wiklander
Browse files

tee: amdtee: fix use-after-free vulnerability in amdtee_close_session 



There is a potential race condition in amdtee_close_session that may
cause use-after-free in amdtee_open_session. For instance, if a session
has refcount == 1, and one thread tries to free this session via:

    kref_put(&sess->refcount, destroy_session);

the reference count will get decremented, and the next step would be to
call destroy_session(). However, if in another thread,
amdtee_open_session() is called before destroy_session() has completed
execution, alloc_session() may return 'sess' that will be freed up
later in destroy_session() leading to use-after-free in
amdtee_open_session.

To fix this issue, treat decrement of sess->refcount and removal of
'sess' from session list in destroy_session() as a critical section, so
that it is executed atomically.

Fixes: 757cc3e9 ("tee: add AMD-TEE driver")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarRijo Thomas <Rijo-john.Thomas@amd.com>
Reviewed-by: default avatarSumit Garg <sumit.garg@linaro.org>
Signed-off-by: default avatarJens Wiklander <jens.wiklander@linaro.org>
parent 2dde18cd

drivers/tee/amdtee/core.c

+6 −4
Original line number Diff line number Diff line
@@ -217,12 +217,12 @@ static int copy_ta_binary(struct tee_context *ctx, void *ptr, void **ta, 
	return rc;

}



/* mutex must be held by caller */

static void destroy_session(struct kref *ref)

{

	struct amdtee_session *sess = container_of(ref, struct amdtee_session,

						   refcount);



	mutex_lock(&session_list_mutex);

	list_del(&sess->list_node);

	mutex_unlock(&session_list_mutex);

	kfree(sess);
@@ -272,7 +272,8 @@ int amdtee_open_session(struct tee_context *ctx, 
	if (arg->ret != TEEC_SUCCESS) {

		pr_err("open_session failed %d\n", arg->ret);

		handle_unload_ta(ta_handle);

		kref_put(&sess->refcount, destroy_session);

		kref_put_mutex(&sess->refcount, destroy_session,

			       &session_list_mutex);

		goto out;

	}
@@ -290,7 +291,8 @@ int amdtee_open_session(struct tee_context *ctx, 
		pr_err("reached maximum session count %d\n", TEE_NUM_SESSIONS);

		handle_close_session(ta_handle, session_info);

		handle_unload_ta(ta_handle);

		kref_put(&sess->refcount, destroy_session);

		kref_put_mutex(&sess->refcount, destroy_session,

			       &session_list_mutex);

		rc = -ENOMEM;

		goto out;

	}
@@ -331,7 +333,7 @@ int amdtee_close_session(struct tee_context *ctx, u32 session) 
	handle_close_session(ta_handle, session_info);

	handle_unload_ta(ta_handle);



	kref_put(&sess->refcount, destroy_session);

	kref_put_mutex(&sess->refcount, destroy_session, &session_list_mutex);



	return 0;

}