Re: [PATCH 1/1] tee: amdtee: fix use-after-free vulnerability in amdtee_close_session

Hi Rijo,

On Fri, 22 Sept 2023 at 12:26, Rijo Thomas Rijo-john.Thomas@amd.com wrote:

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 invocation of destroy_session() as a single critical section, so that it is executed atomically.

Fixes: 757cc3e9ff1d ("tee: add AMD-TEE driver") Cc: stable@vger.kernel.org Signed-off-by: Rijo Thomas Rijo-john.Thomas@amd.com

---

drivers/tee/amdtee/core.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/tee/amdtee/core.c b/drivers/tee/amdtee/core.c index 372d64756ed6..04cee03bec9d 100644 --- a/drivers/tee/amdtee/core.c +++ b/drivers/tee/amdtee/core.c @@ -217,14 +217,13 @@ 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 +271,9 @@ 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);

•           mutex_lock(&session_list_mutex);
            kref_put(&sess->refcount, destroy_session);
  

How about you rather use kref_put_mutex() here and then keep the mutex_unlock() within the destroy_session()?

•           mutex_unlock(&session_list_mutex);
            goto out;
    }
  
  

@@ -290,7 +291,9 @@ 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);

•           mutex_lock(&session_list_mutex);
            kref_put(&sess->refcount, destroy_session);
  

Ditto.

•           mutex_unlock(&session_list_mutex);
            rc = -ENOMEM;
            goto out;
    }
  

@@ -331,7 +334,9 @@ int amdtee_close_session(struct tee_context *ctx, u32 session) handle_close_session(ta_handle, session_info); handle_unload_ta(ta_handle);

•   mutex_lock(&session_list_mutex);
    kref_put(&sess->refcount, destroy_session);
  

Ditto.

-Sumit

•   mutex_unlock(&session_list_mutex);
  
    return 0;
  

}

2.25.1