From: Stefan Haberland sth@linux.ibm.com
commit db7ba07108a48c0f95b74fabbfd5d63e924f992d upstream.
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 Link: https://lore.kernel.org/r/20220919154931.4123002-2-sth@linux.ibm.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/s390/block/dasd_alias.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
--- 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 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 }
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)) {