[PATCH 6.1 111/131] tee: amdtee: fix use-after-free vulnerability in amdtee_close_session

Greg Kroah-Hartman
2023-10-16T09:03:18Z

From: Rijo Thomas <Rijo-john.Thomas@amd.com>

commit f4384b3e54ea813868bb81a861bf5b2406e15d8f upstream.

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: 757cc3e9ff1d ("tee: add AMD-TEE driver")
Cc: stable@vger.kernel.org
Signed-off-by: Rijo Thomas <Rijo-john.Thomas@amd.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tee/amdtee/core.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/tee/amdtee/core.c
+++ b/drivers/tee/amdtee/core.c
@@ -217,12 +217,12 @@ unlock:
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_conte
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_conte
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_cont
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;
}