linux-kernel - Re: [PATCH 5.10 191/717] memstick: fix a double-free bug in memstick

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Date:   Tue, 29 Dec 2020 23:42:02 +0100
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Hulk Robot <hulkci@...wei.com>,
        Qinglang Miao <miaoqinglang@...wei.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 191/717] memstick: fix a double-free bug in
 memstick_check

Hi!

> From: Qinglang Miao <miaoqinglang@...wei.com>
> 
> [ Upstream commit e3e9ced5c93803d5b2ea1942c4bf0192622531d6 ]
> 
> kfree(host->card) has been called in put_device so that
> another kfree would raise cause a double-free bug.

> +++ b/drivers/memstick/core/memstick.c
> @@ -468,7 +468,6 @@ static void memstick_check(struct work_struct *work)
>  			host->card = card;
>  			if (device_register(&card->dev)) {
>  				put_device(&card->dev);
> -				kfree(host->card);
>  				host->card = NULL;
>  			}

Does the host->card = NULL need to be removed, too (and following code
refactored)? put_device() needs that pointer to be able to free it and
it can do so asynchronously.

This will cause crashes; they should be easy to reproduce with
CONFIG_DEBUG_KOBJECT_RELEASE due to delay in kobject_release() AFAICT.

Best regards,								Pavel

-- 
http://www.livejournal.com/~pavelmachek

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