+ rapidio-mport_cdev-fix-use-after-free-in-dma_req_free.patch added to mm-nonmm-unstable branch

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

The patch titled
     Subject: rapidio: mport_cdev: fix use-after-free in dma_req_free()
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     rapidio-mport_cdev-fix-use-after-free-in-dma_req_free.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/rapidio-mport_cdev-fix-use-after-free-in-dma_req_free.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: James Kim <james010kim@gmail.com>
Subject: rapidio: mport_cdev: fix use-after-free in dma_req_free()
Date: Fri, 24 Jul 2026 08:52:20 +0900

dma_req_free() acquires buf_mutex through req->map, drops the mapping
reference with kref_put(), and then dereferences req->map again to unlock
the mutex.

If kref_put() drops the last reference, mport_release_mapping() frees the
mapping, and the subsequent mutex_unlock() dereferences a freed object. 
This is a use-after-free.

Fix this by caching map and md before kref_put(), clearing req->map while
holding buf_mutex, and using the cached md for mutex unlocking.

The bug is reachable from userspace via the RapidIO mport character device
interface.

Link: https://lore.kernel.org/20260723235220.588424-1-james010kim@gmail.com
Fixes: e8de370188d0 ("rapidio: add mport char device driver")
Signed-off-by: James Kim <james010kim@gmail.com>
Reviewed-by: Dan Carpenter <error27@gmail.com>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/rapidio/devices/rio_mport_cdev.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/rapidio/devices/rio_mport_cdev.c~rapidio-mport_cdev-fix-use-after-free-in-dma_req_free
+++ a/drivers/rapidio/devices/rio_mport_cdev.c
@@ -564,9 +564,13 @@ static void dma_req_free(struct kref *re
 	}
 
 	if (req->map) {
-		mutex_lock(&req->map->md->buf_mutex);
-		kref_put(&req->map->ref, mport_release_mapping);
-		mutex_unlock(&req->map->md->buf_mutex);
+		struct rio_mport_mapping *map = req->map;
+		struct mport_dev *md = map->md;
+
+		mutex_lock(&md->buf_mutex);
+		req->map = NULL;
+		kref_put(&map->ref, mport_release_mapping);
+		mutex_unlock(&md->buf_mutex);
 	}
 
 	kref_put(&priv->dma_ref, mport_release_dma);
_

Patches currently in -mm which might be from james010kim@gmail.com are

rapidio-mport_cdev-fix-use-after-free-in-dma_req_free.patch