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From: Andrew Morton <akpm@linux-foundation.org>
To: Oscar Salvador <osalvador@suse.de>
Cc: n-horiguchi@ah.jp.nec.com, vbabka@suse.cz,
	dan.j.williams@intel.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm,memory_failure: Always pin the page in madvise_inject_error
Date: Mon, 7 Dec 2020 18:22:00 -0800	[thread overview]
Message-ID: <20201207182200.21f97d90211c78609ffd7351@linux-foundation.org> (raw)
In-Reply-To: <20201207094818.8518-1-osalvador@suse.de>

On Mon,  7 Dec 2020 10:48:18 +0100 Oscar Salvador <osalvador@suse.de> wrote:

> madvise_inject_error() uses get_user_pages_fast to translate the
> address we specified to a page.
> After [1], we drop the extra reference count for memory_failure() path.
> That commit says that memory_failure wanted to keep the pin in order
> to take the page out of circulation.
> 
> The truth is that we need to keep the page pinned, otherwise the
> page might be re-used after the put_page() and we can end up messing
> with someone else's memory.
> 
> E.g:
> 
> CPU0
> process X					CPU1
>  madvise_inject_error
>   get_user_pages
>    put_page
> 					page gets reclaimed
> 					process Y allocates the page
>   memory_failure
>    // We mess with process Y memory
> 
> madvise() is meant to operate on a self address space, so messing with
> pages that do not belong to us seems the wrong thing to do.
> To avoid that, let us keep the page pinned for memory_failure as well.
> 
> Pages for DAX mappings will release this extra refcount in
> memory_failure_dev_pagemap.

Does the bug have any known user-visible effects?  Is a deliberate
exploit conceivable?

IOW, cc:stable and if so, why?


  reply	other threads:[~2020-12-08  2:22 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-07  9:48 [PATCH] mm,memory_failure: Always pin the page in madvise_inject_error Oscar Salvador
2020-12-08  2:22 ` Andrew Morton [this message]
2020-12-08  2:34   ` HORIGUCHI NAOYA(堀口　直也)
2020-12-08  2:35 ` HORIGUCHI NAOYA(堀口　直也)

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