Re: [PATCH 5.10 540/545] tee: add overflow check in register_shm_helper()

[Pavel Machek]

Hi!

> From: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> 
> commit 573ae4f13f630d6660008f1974c0a8a29c30e18a upstream.
> 
> With special lengths supplied by user space, register_shm_helper() has
> an integer overflow when calculating the number of pages covered by a
> supplied user space memory region.
> 
> This causes internal_get_user_pages_fast() a helper function of
> pin_user_pages_fast() to do a NULL pointer dereference:

Maybe this needs fixing, but this fix adds a memory leak or two. Note
the goto err, that needs to be done.

Best regards,
								Pavel

Signed-off-by: Pavel Machek <pavel@xxxxxxx>

> +++ b/drivers/tee/tee_shm.c
> @@ -222,6 +222,9 @@ struct tee_shm *tee_shm_register(struct
>  		goto err;
>  	}
>  
> +	if (!access_ok((void __user *)addr, length))
> +		return ERR_PTR(-EFAULT);
> +
>  	mutex_lock(&teedev->mutex);
>  	shm->id = idr_alloc(&teedev->idr, shm, 1, 0, GFP_KERNEL);
>  	mutex_unlock(&teedev->mutex);
> 


diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index 6e662fb131d5..283fa50676a2 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -222,8 +222,10 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
 		goto err;
 	}
 
-	if (!access_ok((void __user *)addr, length))
-		return ERR_PTR(-EFAULT);
+	if (!access_ok((void __user *)addr, length)) {
+		ret = ERR_PTR(-EFAULT);
+		goto err;
+	}
 
 	mutex_lock(&teedev->mutex);
 	shm->id = idr_alloc(&teedev->idr, shm, 1, 0, GFP_KERNEL);

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