Re: [PATCH 1/1] staging: ion: Prevent incorrect reference counting behavour

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

On Thu, Nov 25, 2021 at 06:18:22PM +0300, Dan Carpenter wrote:
> I had thought that ->kmap_cnt was a regular int and not an unsigned
> int, but I would have to pull a stable tree to see where I misread the
> code.

I was looking at (struct ion_buffer)->kmap_cnt but this is
(struct ion_handle)->kmap_cnt.  I'm not sure how those are related but
it makes me nervous that one can go higher than the other.  Also both
probably need overflow protection.

So I guess I would just do something like:

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index 806e9b30b9dc8..e8846279b33b5 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -489,6 +489,8 @@ static void *ion_buffer_kmap_get(struct ion_buffer *buffer)
 	void *vaddr;
 
 	if (buffer->kmap_cnt) {
+		if (buffer->kmap_cnt == INT_MAX)
+			return ERR_PTR(-EOVERFLOW);
 		buffer->kmap_cnt++;
 		return buffer->vaddr;
 	}
@@ -509,6 +511,8 @@ static void *ion_handle_kmap_get(struct ion_handle *handle)
 	void *vaddr;
 
 	if (handle->kmap_cnt) {
+		if (handle->kmap_cnt == INT_MAX)
+			return ERR_PTR(-EOVERFLOW);
 		handle->kmap_cnt++;
 		return buffer->vaddr;
 	}