linux-kernel - Re: [PATCH] prctl: fix PR_SET_MM

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Message-ID: <20210315120803.GA13620@redhat.com>
Date:   Mon, 15 Mar 2021 13:08:03 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        gorcunov@...nvz.org, security@...nel.org
Subject: Re: [PATCH] prctl: fix PR_SET_MM_AUXV kernel stack leak

On 03/14, Alexey Dobriyan wrote:
>
> 	prctl(PR_SET_MM, PR_SET_MM_AUXV, addr, 1);
>
> will copy 1 byte from userspace to (quite big) on-stack array
> and then stash everything to mm->saved_auxv.

I too don't understand, memcpy(mm->saved_auxv, user_auxv, len) will
copy 1 byte...

And why task_lock(current) ? What does it try to protect?

Oleg.