[PATCH 1/4] master - libmultipath: fix use after free when iscsi logs in

[mwilck@xxxxxxxx]

From: lixiaokeng <lixiaokeng@xxxxxxxxxx>

When two iscsi ips log in and out alternately and  the following scripts run
at the same time,

#!/bin/bash
interval=5
while true
do
        iscsiadm -m node -p 9.41.147.171 &> /dev/null
        iscsiadm -m node -p 9.41.148.172 &> /dev/null
        iscsiadm -m session &> /dev/null
        rescan-scsi-bus.sh &> /dev/null
        multipath -v2 &> /dev/null
        multipath -ll &> /dev/null
        sleep $interval
done

multipathd will have a segfault after about 30 mins.

The reason is that mpp->hwe is accessed after hwe is already freed. In
extract_hwe_from_path func, mpp->hwe is set to pp->hwe, so they points to the
same hwe. For some reasons, pp->mpp will be set to NULL in orphan_path func.
Then, pp and hwe will be freed with (pp->mpp == NULL) in free_path func
called by ev_remove_path func. However, mpp->hwe is not set to NULL while hwe
is already freed. So, when iscsi device logs in and new path is added to mpp,
mpp->hwe will be accessed in select_pgfailback func. Finally, use-after-free
problem occurs.

The procedure details given as follows,
1.wait_dmevents thread
wait_dmevents
	->dmevent_loop
		->update_multipath
			->__setup_multipath
				->update_multipath_strings
					 -> sync_paths
						->orphan_path
2.uevqloop thread  (iscsi log out, remove path)
uevqloop
->uevent_dispatch
	->service_uevq
		->uev_remove_path
			->ev_remove_path  //pp->mpp is NULL
				->free_path(pp)
			//pp->hew are freed but mpp->hwe is not set to NULL
3.ev_remove_path  (iscsi log in, add path)
uevqloop
->uevent_dispatch
	->service_uevq
		->ev_add_path
			->select_pgfailback //mpp->hwe is accessed

Here, we will set mpp->hwe to NULL before setting pp->map to NULL in orphan_path
func.

Signed-off-by: Tianxiong Lu <lutianxiong@xxxxxxxxxx>
Signed-off-by: lixiaokeng <lixiaokeng@xxxxxxxxxx>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@xxxxxxxxxx>
Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
---
 libmultipath/structs_vec.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libmultipath/structs_vec.c b/libmultipath/structs_vec.c
index 3dbbaa0..9bbe5d1 100644
--- a/libmultipath/structs_vec.c
+++ b/libmultipath/structs_vec.c
@@ -93,6 +93,8 @@ int adopt_paths(vector pathvec, struct multipath *mpp)
 void orphan_path(struct path *pp, const char *reason)
 {
 	condlog(3, "%s: orphan path, %s", pp->dev, reason);
+	if (pp->mpp && pp->mpp->hwe == pp->hwe)
+		pp->mpp->hwe = NULL;
 	pp->mpp = NULL;
 	pp->dmstate = PSTATE_UNDEF;
 	pp->uid_attribute = NULL;
-- 
2.26.2


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