From 5cbef379a94b161726c5f504598bf4791d45cedc Mon Sep 17 00:00:00 2001 From: James Kim Date: Fri, 24 Jul 2026 08:52:20 +0900 Subject: [PATCH] rapidio: mport_cdev: fix use-after-free in dma_req_free() 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 Reviewed-by: Dan Carpenter Cc: Alexandre Bounine Cc: Greg Kroah-Hartman Cc: Matt Porter Cc: Signed-off-by: Andrew Morton --- drivers/rapidio/devices/rio_mport_cdev.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c index 009b3b595bbf..ad82c2108a56 100644 --- a/drivers/rapidio/devices/rio_mport_cdev.c +++ b/drivers/rapidio/devices/rio_mport_cdev.c @@ -564,9 +564,13 @@ static void dma_req_free(struct kref *ref) } 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);