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Date:   Sat, 15 Jun 2019 13:32:41 -0700 (PDT)
Message-Id: <20190615.133241.1697724537695155418.davem@davemloft.net>
To:     houjingyi647@gmail.com
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix double-fetch bug in sock_getsockopt()
From:   David Miller <davem@davemloft.net>
In-Reply-To: <20190613104457.GA6296@hjy-HP-Notebook>
References: <20190613104457.GA6296@hjy-HP-Notebook>
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From: JingYi Hou <houjingyi647@gmail.com>
Date: Thu, 13 Jun 2019 18:44:57 +0800

> In sock_getsockopt(), 'optlen' is fetched the first time from userspace.
> 'len < 0' is then checked. Then in condition 'SO_MEMINFO', 'optlen' is
> fetched the second time from userspace without check.
> 
> if a malicious user can change it between two fetches may cause security
> problems or unexpected behaivor.
> 
> To fix this, we need to recheck it in the second fetch.
> 
> Signed-off-by: JingYi Hou <houjingyi647@gmail.com>

THere is no reason to fetch len a second time, so please just remove
the get_user() call here instead.

Also, please format your Subject line properly with appropriate subsystem
prefixes etc.