From: Ioanna Alifieraki <ioanna-maria.alifieraki@xxxxxxxxxxxxx> commit 1d49eb91e86e8c1c1614c72e3e958b6b7e2472a9 upstream. Currently when removing an ipmi_user the removal is deferred as a work on the system's workqueue. Although this guarantees the free operation will occur in non atomic context, it can race with the ipmi_msghandler module removal (see [1]) . In case a remove_user work is scheduled for removal and shortly after ipmi_msghandler module is removed we can end up in a situation where the module is removed fist and when the work is executed the system crashes with : BUG: unable to handle page fault for address: ffffffffc05c3450 PF: supervisor instruction fetch in kernel mode PF: error_code(0x0010) - not-present page because the pages of the module are gone. In cleanup_ipmi() there is no easy way to detect if there are any pending works to flush them before removing the module. This patch creates a separate workqueue and schedules the remove_work works on it. When removing the module the workqueue is drained when destroyed to avoid the race. [1] https://bugs.launchpad.net/bugs/1950666 Cc: stable@xxxxxxxxxxxxxxx # 5.1 Fixes: 3b9a907223d7 (ipmi: fix sleep-in-atomic in free_user at cleanup SRCU user->release_barrier) Signed-off-by: Ioanna Alifieraki <ioanna-maria.alifieraki@xxxxxxxxxxxxx> Message-Id: <20211115131645.25116-1-ioanna-maria.alifieraki@xxxxxxxxxxxxx> Signed-off-by: Corey Minyard <cminyard@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/char/ipmi/ipmi_msghandler.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) --- a/drivers/char/ipmi/ipmi_msghandler.c +++ b/drivers/char/ipmi/ipmi_msghandler.c @@ -203,6 +203,8 @@ struct ipmi_user { struct work_struct remove_work; }; +struct workqueue_struct *remove_work_wq; + static struct ipmi_user *acquire_ipmi_user(struct ipmi_user *user, int *index) __acquires(user->release_barrier) { @@ -1272,7 +1274,7 @@ static void free_user(struct kref *ref) struct ipmi_user *user = container_of(ref, struct ipmi_user, refcount); /* SRCU cleanup must happen in task context. */ - schedule_work(&user->remove_work); + queue_work(remove_work_wq, &user->remove_work); } static void _ipmi_destroy_user(struct ipmi_user *user) @@ -5166,6 +5168,13 @@ static int ipmi_init_msghandler(void) atomic_notifier_chain_register(&panic_notifier_list, &panic_block); + remove_work_wq = create_singlethread_workqueue("ipmi-msghandler-remove-wq"); + if (!remove_work_wq) { + pr_err("unable to create ipmi-msghandler-remove-wq workqueue"); + rv = -ENOMEM; + goto out; + } + initialized = true; out: @@ -5191,6 +5200,8 @@ static void __exit cleanup_ipmi(void) int count; if (initialized) { + destroy_workqueue(remove_work_wq); + atomic_notifier_chain_unregister(&panic_notifier_list, &panic_block);
