[PATCH v2] RDMA/rtrs: Fix use-after-free in path files cleanup

[Guangshuo Li <lgs201920130244@gmail.com>]

Once kobject_put() is called on srv_path->kobj, the release callback may be
triggered and srv_path may be freed. Therefore, srv_path must not be used
after kobject_put(&srv_path->kobj).

Both rtrs_srv_create_path_files() and rtrs_srv_destroy_path_files()
currently call rtrs_srv_destroy_once_sysfs_root_folders(srv_path) after
kobject_put(&srv_path->kobj). Although the call site only passes srv_path
as an argument, rtrs_srv_destroy_once_sysfs_root_folders() dereferences it
internally to access srv_path->srv. If kobject_put() has already freed
srv_path, this results in a use-after-free.

Move rtrs_srv_destroy_once_sysfs_root_folders() before kobject_put(), so
srv_path remains valid while the helper accesses it.

This issue was found by a static analysis tool I am developing.

Fixes: ae4c81644e91 ("RDMA/rtrs-srv: Rename rtrs_srv_sess to rtrs_srv_path")
Acked-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
v2:
  - Clarify that the use-after-free happens inside
    rtrs_srv_destroy_once_sysfs_root_folders(), which dereferences srv_path
    after kobject_put() may have freed it.
  - No code changes.

 drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c b/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c
index 51727c7d710c..c9ba9d2d0eb3 100644
--- a/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c
@@ -295,8 +295,8 @@ int rtrs_srv_create_path_files(struct rtrs_srv_path *srv_path)
 put_kobj:
 	kobject_del(&srv_path->kobj);
 destroy_root:
-	kobject_put(&srv_path->kobj);
 	rtrs_srv_destroy_once_sysfs_root_folders(srv_path);
+	kobject_put(&srv_path->kobj);
 
 	return err;
 }
@@ -312,8 +312,8 @@ void rtrs_srv_destroy_path_files(struct rtrs_srv_path *srv_path)
 
 	if (srv_path->kobj.state_in_sysfs) {
 		sysfs_remove_group(&srv_path->kobj, &rtrs_srv_path_attr_group);
-		kobject_put(&srv_path->kobj);
 		rtrs_srv_destroy_once_sysfs_root_folders(srv_path);
+		kobject_put(&srv_path->kobj);
 	}
 
 }
-- 
2.43.0