[PATCH 6.12 119/567] ipmi: Fix the race between __scan_channels() and deliver_response()

Greg Kroah-Hartman
2026-01-06T17:20:47Z

From: Jinhui Guo <guojinhui.liam@bytedance.com>

[ Upstream commit 936750fdba4c45e13bbd17f261bb140dd55f5e93 ]

The race window between __scan_channels() and deliver_response() causes
the parameters of some channels to be set to 0.

1.[CPUA] __scan_channels() issues an IPMI request and waits with
wait_event() until all channels have been scanned.
wait_event() internally calls might_sleep(), which might
yield the CPU. (Moreover, an interrupt can preempt
wait_event() and force the task to yield the CPU.)
2.[CPUB] deliver_response() is invoked when the CPU receives the
IPMI response. After processing a IPMI response,
deliver_response() directly assigns intf->wchannels to
intf->channel_list and sets intf->channels_ready to true.
However, not all channels are actually ready for use.
3.[CPUA] Since intf->channels_ready is already true, wait_event()
never enters __wait_event(). __scan_channels() immediately
clears intf->null_user_handler and exits.
4.[CPUB] Once intf->null_user_handler is set to NULL, deliver_response()
ignores further IPMI responses, leaving the remaining
channels zero-initialized and unusable.

CPUA CPUB
------------------------------- -----------------------------
__scan_channels()
intf->null_user_handler
= channel_handler;
send_channel_info_cmd(intf,
0);
wait_event(intf->waitq,
intf->channels_ready);
do {
might_sleep();
deliver_response()
channel_handler()
intf->channel_list =
intf->wchannels + set;
intf->channels_ready = true;
send_channel_info_cmd(intf,
intf->curr_channel);
if (condition)
break;
__wait_event(wq_head,
condition);
} while(0)
intf->null_user_handler
= NULL;
deliver_response()
if (!msg->user)
if (intf->null_user_handler)
rv = -EINVAL;
return rv;
------------------------------- -----------------------------

Fix the race between __scan_channels() and deliver_response() by
deferring both the assignment intf->channel_list = intf->wchannels
and the flag intf->channels_ready = true until all channels have
been successfully scanned or until the IPMI request has failed.

Signed-off-by: Jinhui Guo <guojinhui.liam@bytedance.com>
Message-ID: <20250930074239.2353-2-guojinhui.liam@bytedance.com>
Signed-off-by: Corey Minyard <corey@minyard.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/char/ipmi/ipmi_msghandler.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 99fe01321971..29106325aba7 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -3414,8 +3414,6 @@ channel_handler(struct ipmi_smi *intf, struct ipmi_recv_msg *msg)
intf->channels_ready = true;
wake_up(&intf->waitq);
} else {
- intf->channel_list = intf->wchannels + set;
- intf->channels_ready = true;
rv = send_channel_info_cmd(intf, intf->curr_channel);
}

--
2.51.0