tee: amdtee: fix race condition in amdtee_open_session

There is a potential race condition in amdtee_open_session that may
lead to use-after-free. For instance, in amdtee_open_session() after
sess->sess_mask is set, and before setting:

    sess->session_info[i] = session_info;

if amdtee_close_session() closes this same session, then 'sess' data
structure will be released, causing kernel panic when 'sess' is
accessed within amdtee_open_session().

The solution is to set the bit sess->sess_mask as the last step in
amdtee_open_session().

Fixes: 757cc3e9ff1d ("tee: add AMD-TEE driver")
Cc: stable@vger.kernel.org
Signed-off-by: Rijo Thomas <Rijo-john.Thomas@amd.com>
Acked-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

diff --git a/drivers/tee/amdtee/core.c b/drivers/tee/amdtee/core.c
index 297dc62bca2986f014c4b4060c95d112a807fe7d..372d64756ed64b10c3dd9096aa20886320837ff9 100644 (file)
--- a/drivers/tee/amdtee/core.c
+++ b/drivers/tee/amdtee/core.c
@@ -267,35 +267,34 @@ int amdtee_open_session(struct tee_context *ctx,
                goto out;
        }
 
+       /* Open session with loaded TA */
+       handle_open_session(arg, &session_info, param);
+       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);
+               goto out;
+       }
+
        /* Find an empty session index for the given TA */
        spin_lock(&sess->lock);
        i = find_first_zero_bit(sess->sess_mask, TEE_NUM_SESSIONS);
-       if (i < TEE_NUM_SESSIONS)
+       if (i < TEE_NUM_SESSIONS) {
+               sess->session_info[i] = session_info;
+               set_session_id(ta_handle, i, &arg->session);
                set_bit(i, sess->sess_mask);
+       }
        spin_unlock(&sess->lock);
 
        if (i >= TEE_NUM_SESSIONS) {
                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);
                rc = -ENOMEM;
                goto out;
        }
 
-       /* Open session with loaded TA */
-       handle_open_session(arg, &session_info, param);
-       if (arg->ret != TEEC_SUCCESS) {
-               pr_err("open_session failed %d\n", arg->ret);
-               spin_lock(&sess->lock);
-               clear_bit(i, sess->sess_mask);
-               spin_unlock(&sess->lock);
-               handle_unload_ta(ta_handle);
-               kref_put(&sess->refcount, destroy_session);
-               goto out;
-       }
-
-       sess->session_info[i] = session_info;
-       set_session_id(ta_handle, i, &arg->session);
 out:
        free_pages((u64)ta, get_order(ta_size));
        return rc;