Re: [PATCH] rapidio: mport_cdev: fix use-after-free in mport_mm_close()

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 14 Sep 2026 13:23:27 +0900 James Kim <james010kim@gmail.com> wrote:

> A use-after-free vulnerability was identified in mport_mm_close() in
> drivers/rapidio/devices/rio_mport_cdev.c, identical to the pattern
> previously addressed in dma_req_free().
> 
> This is observable from userspace when an application creates an mmap
> mapping via the RapidIO character device and subsequently unmaps it
> (or terminates, triggering exit_mmap()). During munmap, mport_mm_close()
> is invoked and drops the mapping reference via kref_put().
> 
> If kref_put() drops the last reference, mport_release_mapping() is called,
> which frees the underlying rio_mport_mapping structure. The subsequent
> mutex_unlock() then dereferences map->md to unlock buf_mutex, leading to
> a use-after-free:
> 
>    mport_mm_close()
>      -> mutex_lock(&map->md->buf_mutex);
>      ...
>      -> kref_put(&map->ref, mport_release_mapping); /* map is freed */
>      -> mutex_unlock(&map->md->buf_mutex);          /* UAF: map used */
> 
> Fix this by caching map->md before kref_put() and using the cached
> pointer for mutex unlocking, ensuring that freed memory is not accessed.
> 

Thanks.

> Note for Andrew:
> Following up on the Sashiko review results you shared in the dma_req_free()
> thread (https://sashiko.dev/#/patchset/20260615070530.371640-1-james010kim@gmail.com),
> I audited the reported pre-existing flaws and verified that this UAF in
> mport_mm_close() is a genuine bug with the identical locking pattern.
> 

Thanks again.

Sashiko blew another fuse over the rapidio driver:

	https://sashiko.dev/#/patchset/20260914042327.49798-1-james010kim@gmail.com