rapidio: mport_cdev: fix use-after-free in mport_mm_close()

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.

Link: https://lore.kernel.org/20260914042327.49798-1-james010kim@gmail.com
Fixes: e8de370188d0 ("rapidio: add mport char device driver")
Signed-off-by: James Kim <james010kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: <stable@vger.kernel.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
index ad82c2108a56..47ba34b4afb2 100644
--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -2167,11 +2167,12 @@ static void mport_mm_open(struct vm_area_struct *vma)
 static void mport_mm_close(struct vm_area_struct *vma)
 {
 	struct rio_mport_mapping *map = vma->vm_private_data;
+	struct mport_dev *md = map->md;
 
 	rmcd_debug(MMAP, "%pad", &map->phys_addr);
-	mutex_lock(&map->md->buf_mutex);
+	mutex_lock(&md->buf_mutex);
 	kref_put(&map->ref, mport_release_mapping);
-	mutex_unlock(&map->md->buf_mutex);
+	mutex_unlock(&md->buf_mutex);
 }
 
 static const struct vm_operations_struct vm_ops = {