[PATCH 1/1] s390/dasd: fix Oops in dasd_alias_get_start_dev due to missing pavgroup

Stefan Haberland
2022-09-19T15:49:44Z

Fix Oops in dasd_alias_get_start_dev() function caused by the pavgroup
pointer being NULL.

The pavgroup pointer is checked on the entrance of the function but
without the lcu->lock being held. Therefore there is a race window
between dasd_alias_get_start_dev() and _lcu_update() which sets
pavgroup to NULL with the lcu->lock held.

Fix by checking the pavgroup pointer with lcu->lock held.

Cc: <stable@vger.kernel.org> # 2.6.25+
Fixes: 8e09f21574ea ("[S390] dasd: add hyper PAV support to DASD device driver, part 1")
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
---
drivers/s390/block/dasd_alias.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/block/dasd_alias.c b/drivers/s390/block/dasd_alias.c
index dc78a523a69f..b6b938aa6615 100644
--- a/drivers/s390/block/dasd_alias.c
+++ b/drivers/s390/block/dasd_alias.c
@@ -675,12 +675,12 @@ int dasd_alias_remove_device(struct dasd_device *device)
struct dasd_device *dasd_alias_get_start_dev(struct dasd_device *base_device)
{
struct dasd_eckd_private *alias_priv, *private = base_device->private;
- struct alias_pav_group *group = private->pavgroup;
struct alias_lcu *lcu = private->lcu;
struct dasd_device *alias_device;
+ struct alias_pav_group *group;
unsigned long flags;

- if (!group || !lcu)
+ if (!lcu)
return NULL;
if (lcu->pav == NO_PAV ||
lcu->flags & (NEED_UAC_UPDATE | UPDATE_PENDING))
@@ -697,6 +697,11 @@ struct dasd_device *dasd_alias_get_start_dev(struct dasd_device *base_device)
}

spin_lock_irqsave(&lcu->lock, flags);
+ group = private->pavgroup;
+ if (!group) {
+ spin_unlock_irqrestore(&lcu->lock, flags);
+ return NULL;
+ }
alias_device = group->next;
if (!alias_device) {
if (list_empty(&group->aliaslist)) {
--
2.34.1