linux-kernel - Re: [PATCH] futex: Fix fault_in_user

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Message-ID: <20210816182750.26i535ilc6nef5k6@offworld>
Date:   Mon, 16 Aug 2021 11:27:50 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Huacai Chen <chenhuacai@...ngson.cn>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhuacai@...il.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Hongchen Zhang <zhanghongchen@...ngson.cn>
Subject: Re: [PATCH] futex: Fix fault_in_user_writeable()

On Mon, 16 Aug 2021, Huacai Chen wrote:

>fault_in_user_writeable() should verify R/W access but only verify W. In
>most archs W implies R, but not true in MIPS and LoongArch, so fix it.

Yuck for a find_vma() in futex.c. If this is a problem in MIPS, shouldn't
the fix be there? Furthermore it's stated that fault_in_user_writeable():

"Fault in user address and verify RW access"

And you guys seem to have proposed it already:

https://lore.kernel.org/linux-mips/20200630005845.1239974-1-liulichao@loongson.cn/

Thanks,
Davidlohr