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

[Corey Minyard <corey@minyard.net>]

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.

-corey

> 
> Fixes: b52da4054ee0 ("ipmi: Rework user message limit handling")
> Reported-by: Eric Dumazet <edumazet@google.com>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Greg Thelen <gthelen@google.com>
> Signed-off-by: Guenter Roeck <linux@roeck-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
>