linux-kernel - [PATCH] ipmi: fix unsigned long underflow

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Message-Id: <1501381228-30958-1-git-send-email-minyard@acm.org>
Date:   Sat, 29 Jul 2017 21:20:28 -0500
From:   minyard@....org
To:     Weilong Chen <chenweilong@...wei.com>
Cc:     openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Corey Minyard <cminyard@...sta.com>
Subject: [PATCH] ipmi: fix unsigned long underflow

From: Corey Minyard <cminyard@...sta.com>

When I set the timeout to a specific value such as 500ms, the timeout
event will not happen in time due to the overflow in function
check_msg_timeout:
...
	ent->timeout -= timeout_period;
	if (ent->timeout > 0)
		return;
...

The type of timeout_period is long, but ent->timeout is unsigned long.
This patch makes the type consistent.

Reported-by: Weilong Chen <chenweilong@...wei.com>
Signed-off-by: Corey Minyard <cminyard@...sta.com>
---
I like to keep things consistent (though I obviously messed up here)
and keep variables that should be positive unsigned.

But you are right, there is a bug here and some inconsistency.
This patch changes timeout_period to be unsigned and fixes the
check.  Can you try this out?

 drivers/char/ipmi/ipmi_msghandler.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 810b138..c82d9fd 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -4030,7 +4030,8 @@ smi_from_recv_msg(ipmi_smi_t intf, struct ipmi_recv_msg *recv_msg,
 }
 
 static void check_msg_timeout(ipmi_smi_t intf, struct seq_table *ent,
-			      struct list_head *timeouts, long timeout_period,
+			      struct list_head *timeouts,
+			      unsigned long timeout_period,
 			      int slot, unsigned long *flags,
 			      unsigned int *waiting_msgs)
 {
@@ -4043,8 +4044,8 @@ static void check_msg_timeout(ipmi_smi_t intf, struct seq_table *ent,
 	if (!ent->inuse)
 		return;
 
-	ent->timeout -= timeout_period;
-	if (ent->timeout > 0) {
+	if (timeout_period < ent->timeout) {
+		ent->timeout -= timeout_period;
 		(*waiting_msgs)++;
 		return;
 	}
@@ -4110,7 +4111,8 @@ static void check_msg_timeout(ipmi_smi_t intf, struct seq_table *ent,
 	}
 }
 
-static unsigned int ipmi_timeout_handler(ipmi_smi_t intf, long timeout_period)
+static unsigned int ipmi_timeout_handler(ipmi_smi_t intf,
+					 unsigned long timeout_period)
 {
 	struct list_head     timeouts;
 	struct ipmi_recv_msg *msg, *msg2;
-- 
2.7.4