linux-kernel - Re: [PATCH] ipmi: Fix handling of messages with provided receive message pointer

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Message-ID: <aOT9o-IkilgQXktF@mail.minyard.net>
Date: Tue, 7 Oct 2025 06:46:43 -0500
From: Corey Minyard <corey@...yard.net>
To: Guenter Roeck <linux@...ck-us.net>,
	openipmi-developer@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Greg Thelen <gthelen@...gle.com>
Subject: Re: [PATCH] ipmi: Fix handling of messages with provided receive
 message pointer

On Tue, Oct 07, 2025 at 06:46:01AM -0500, Corey Minyard wrote:
> On Mon, Oct 06, 2025 at 01:18:57PM -0700, Guenter Roeck wrote:
> > Prior to commit b52da4054ee0 ("ipmi: Rework user message limit handling"),
> > i_ipmi_request() used to increase the user reference counter if the receive
> > message is provided by the caller of IPMI API functions. This is no longer
> > the case. However, ipmi_free_recv_msg() is still called and decreases the
> > reference counter. This results in the reference counter reaching zero,
> > the user data pointer is released, and all kinds of interesting crashes are
> > seen.
> > 
> > Fix the problem by increasing user reference counter if the receive message
> > has been provided by the caller.
> 
> Yes, the only interface that uses this that would matter is the watchdog
> timer, which my tests don't currently cover.  I guess I need to add some
> tests.
> 
> Sorry, and thanks for the fix.  It's queued for next release.

Sorry, it's queued for this release, 6.18.  I'll send it to Linus
in a few days.

-corey

> 
> -corey
> 
> > 
> > Fixes: b52da4054ee0 ("ipmi: Rework user message limit handling")
> > Reported-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Cc: Greg Thelen <gthelen@...gle.com>
> > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > ---
> >  drivers/char/ipmi/ipmi_msghandler.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> > index a0b67a35a5f0..3700ab4eba3e 100644
> > --- a/drivers/char/ipmi/ipmi_msghandler.c
> > +++ b/drivers/char/ipmi/ipmi_msghandler.c
> > @@ -2301,8 +2301,11 @@ static int i_ipmi_request(struct ipmi_user     *user,
> >  	if (supplied_recv) {
> >  		recv_msg = supplied_recv;
> >  		recv_msg->user = user;
> > -		if (user)
> > +		if (user) {
> >  			atomic_inc(&user->nr_msgs);
> > +			/* The put happens when the message is freed. */
> > +			kref_get(&user->refcount);
> > +		}
> >  	} else {
> >  		recv_msg = ipmi_alloc_recv_msg(user);
> >  		if (IS_ERR(recv_msg))
> > -- 
> > 2.45.2
> >