linux-kernel - Re: [PATCH AUTOSEL 4.20 016/117] fanotify: return only user requested event types in event mask

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Message-ID: <CAOQ4uxgwZjyoEOeRRj0eRsPR2+QmyUht0sErtZV=meKcPTDVcA@mail.gmail.com>
Date:   Wed, 9 Jan 2019 08:50:33 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Matthew Bobrowski <mbobrowski@...browski.org>,
        Jan Kara <jack@...e.cz>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL 4.20 016/117] fanotify: return only user requested
 event types in event mask

On Tue, Jan 8, 2019 at 10:11 PM Sasha Levin <sashal@...nel.org> wrote:
>
> From: Matthew Bobrowski <mbobrowski@...browski.org>
>
> [ Upstream commit 2d10b23082a7eb8be508b3789f2e7250a88a5ddb ]
>
> Modify fanotify_should_send_event() so that it now returns a mask for
> an event that contains ONLY flags for the event types that have been
> specifically requested by the user. Flags that may have been included
> within the event mask, but have not been explicitly requested by the
> user will not be present in the returned value.
>
> As an example, given the situation where a user requests events of type
> FAN_OPEN. Traditionally, the event mask returned within an event that
> occurred on a filesystem object that has been marked for monitoring and is
> opened, will only ever have the FAN_OPEN bit set. With the introduction of
> the new flags like FAN_OPEN_EXEC, and perhaps any other future event
> flags, there is a possibility of the returned event mask containing more
> than a single bit set, despite having only requested the single event type.
> Prior to these modifications performed to fanotify_should_send_event(), a
> user would have received a bundled event mask containing flags FAN_OPEN
> and FAN_OPEN_EXEC in the instance that a file was opened for execution via
> execve(), for example. This means that a user would receive event types
> in the returned event mask that have not been requested. This runs the
> possibility of breaking existing systems and causing other unforeseen
> issues.
>
> To mitigate this possibility, fanotify_should_send_event() has been
> modified to return the event mask containing ONLY event types explicitly
> requested by the user. This means that we will NOT report events that the
> user did no set a mask for, and we will NOT report events that the user
> has set an ignore mask for.
>
> The function name fanotify_should_send_event() has also been updated so
> that it's more relevant to what it has been designed to do.
>
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> Signed-off-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---

Sasha,

I have no objection to applying this patch to 4.20, but FYI, it does
not fix anything.
Before introducing FAN_OPEN_EXEC in 5.0-rc1, this patch has no visible effect.

I don't mind if you apply it. It will make stable code closer to
mainline, which is
always a good thing IMO. And FWIW, I think that patch is quite trivial
and low risk.

Thanks,
Amir.