From bd1c06a4f5e2b2c96b9ff09a13983efb2d013b18 Mon Sep 17 00:00:00 2001 From: Masamitsu Yamazaki Date: Mon, 15 Jan 2018 07:58:12 +0000 Subject: [PATCH] ipmi: Clear smi_info->thread to prevent use-after-free during module unload During code inspection, I found an use-after-free possibility during unloading ipmi_si in the polling mode. If start_new_msg() is called after kthread_stop(), the function will try to wake up non-existing kthread using the dangling pointer. Possible scenario is when a new internal message is generated after ipmi_unregister_smi()[*1] and remains after stop_timer_and_thread() in clenaup_one_si() [*2]. Use-after-free could occur as follows depending on BMC replies. cleanup_one_si => ipmi_unregister_smi [*1] => stop_timer_and_thread => kthread_stop(smi_info->thread) [*2] => poll => smi_event_handler => start_new_msg => if (smi_info->thread) wake_up_process(smi_info->thread) <== use-after-free!! Although currently it seems no such message is generated in the polling mode, some changes might introduce that in thefuture. For example in the interrupt mode, disable_si_irq() does that at [*2]. So let's prevent such a critical issue possibility now. Signed-off-by: Yamazaki Masamitsu Signed-off-by: Corey Minyard --- drivers/char/ipmi/ipmi_si_intf.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c index 7499b0cd8326f..6768cb2dd740e 100644 --- a/drivers/char/ipmi/ipmi_si_intf.c +++ b/drivers/char/ipmi/ipmi_si_intf.c @@ -1938,8 +1938,10 @@ static void check_for_broken_irqs(struct smi_info *smi_info) static inline void stop_timer_and_thread(struct smi_info *smi_info) { - if (smi_info->thread != NULL) + if (smi_info->thread != NULL) { kthread_stop(smi_info->thread); + smi_info->thread = NULL; + } smi_info->timer_can_start = false; if (smi_info->timer_running) -- 2.39.5