Re: [PATCH v4 2/3] fanotify: return only user requested event types in event mask

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On Thu, Oct 11, 2018 at 1:42 PM Matthew Bobrowski
<mbobrowski@xxxxxxxxxxxxxx> wrote:
>
> Modified fanotify_should_send_event() so that it now returns a mask for
> a 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@xxxxxxxxxxxxxx>
> ---

I feel that this story could be shorter and less confusing, but
I cannot offer a better version, nor do I object to this version.
Maybe Jan can give it some final touches.

Thanks,
Amir.



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