linux-kernel - Re: data-race in pcpu_alloc / pcpu_nr

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Message-ID: <20220818192852.0934313f@gandalf.local.home>
Date:   Thu, 18 Aug 2022 19:28:52 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Abhishek Shah <abhishek.shah@...umbia.edu>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        Gabriel Ryan <gabe@...columbia.edu>
Subject: Re: data-race in pcpu_alloc / pcpu_nr_pages

On Thu, 18 Aug 2022 18:29:00 -0400
Abhishek Shah <abhishek.shah@...umbia.edu> wrote:

> Hi all,
> 
> We found a race involving the *pcpu_nr_populated *variable. We discovered
> that the racing variable is used in meminfo_proc_show
> <https://elixir.bootlin.com/linux/v5.18-rc5/source/fs/proc/meminfo.c#L123>,
> but we were not sure if there were other security-relevant implications of
> this race. Please let us know what you think.

So you see that the number displayed in meminfo can be written to while
it's being read?  As it's a long value, it is likely to be accurate (the
value before or after the update). pcpu_nr_pages() is only used to display
the number of pages in meminfo.

I don't see any problem here.

-- Steve