From: Matthew Bobrowski <email@example.com>
To: Amir Goldstein <firstname.lastname@example.org>
Cc: Jan Kara <email@example.com>, Steve Grubb <firstname.lastname@example.org>,
Subject: Re: [PATCH v2 1/1] fanotify: introduce new event flag FAN_EXEC
Date: Mon, 1 Oct 2018 18:21:36 +1000 [thread overview]
Message-ID: <email@example.com> (raw)
On 28/09/18 15:39, Amir Goldstein wrote:
> On Fri, Sep 28, 2018 at 4:28 AM Matthew Bobrowski
> <firstname.lastname@example.org> wrote:
>> Hi Amir,
>> On 27/9/18 11:57 pm, Amir Goldstein wrote:
>>> [cc: linux-api]
>>> On Thu, Sep 27, 2018 at 4:05 PM Matthew Bobrowski
>>> <email@example.com> wrote:
>>>> This is a reduced version of a patch that I originally submitted a while ago.
>>>> In short, the fanotify API currently does not provide any means for user space
>>>> programs to receive events specifically when a file has been opened with the
>>>> intent to be executed. The FAN_EXEC flag will be set within the event mask when
>>>> a object has been opened with one of the open flags being __FMODE_EXEC.
>>>> diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
>>>> index fd1ce10553bf..aad174c81322 100644
>>>> --- a/include/linux/fsnotify.h
>>>> +++ b/include/linux/fsnotify.h
>>>> @@ -216,6 +216,9 @@ static inline void fsnotify_open(struct file *file)
>>>> if (S_ISDIR(inode->i_mode))
>>>> mask |= FS_ISDIR;
>>>> + if (file->f_flags & __FMODE_EXEC)
>>>> + mask |= FS_EXEC;
>>> I think that may be breaking existing programs that do not expect to see
>>> this bit in the event mask (i.e. if they only requested to see FAN_OPEN).
>> A very good point and is definitely something that did cross my mind while
>> writing this patch.
> My only issue with my own suggestion is that this implicit behavior is harder
> to document than the explicit behavior (i.e. "user will get FAN_EXEC only if
> user sets fanotify_init flag FAN_ENABLE_EXEC"), so I haven't decided which
> I prefer yet - waiting for Jan to weight in on this point.
> The concept of "bonus flags" (flags that you got but did not ask for) is not
> new to inotify (I think you can get IN_ATTRIB if you asked for IN_MODIFY),
> but AFAIKT, it would be new to fanotify.
> OTOH, getting an event that you asked for in the past and since then
> removed the event bit from the mark is not a new behavior. Although this
> is not the same as the implicit global enable flag I proposed.
> The more I write about it, the more I am leaning towards explicit enable...
Hm, I can't think of a good justification as to why something that provides
this type of behavior can't be an explicit enable, and why we'd go for an
implicit enable instead? I really like the idea of having an initialization
flag (i.e. FAN_ENABLE_EXECUTE) that controls whether your program is to
receive events that may potentially contain additional "bonus" flags (i.e.
FAN_EXECUTE), or not. The intent of having a flag of this nature is clear,
it makes sense, and would be a good way to potentially enable/disable any
API features moving forward.
>>> A possible mitigation would be to set a group flag FAN_ENABLE_EXEC
>>> on the first time that user requests the FAN_EXEC event and then
>>> compute the FAN_ALL_OUTGOING_EVENTS at runtime based on that
>>> group flag (see example with FAN_ONDIR in my dev branch ).
>>> Unlike my example, I don't think you have to expose the init flag
>>> FAN_ENABLE_EXEC to users, because it can be set implicitly on the
>>> first FAN_EXEC mark request.
>> Ah yes, I think this is quite elegant and could actually work well. Let me
>> review your suggestions and write an alternative patch using this
>> particular approach.
> If Jan accepts my proposal, you can base your patch on:
Ok, great. I've gone ahead and written an updated patch that adds the
ability for programs to explicitly enable the receiving of events that
contain the "FAN_EXECUTE" bonus flag. Programs will have to provide
"FAN_ENABLE_EXECUTE" as one of their initialization flags when calling
fanotify_init() in order to receive any events where the "FAN_EXECUTE" flag
has been set. I think doing it this way would be a far better solution to
mitigate possibly breaking any existing programs.
You can find the patch here:
These changes are based off your branch 'fanotify_api-v3'. Let me know what
next prev parent reply other threads:[~2018-10-01 14:58 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-27 13:05 [PATCH v2 1/1] fanotify: introduce new event flag FAN_EXEC Matthew Bobrowski
2018-09-27 13:57 ` Amir Goldstein
2018-09-28 1:27 ` Matthew Bobrowski
2018-09-28 5:39 ` Amir Goldstein
2018-10-01 8:21 ` Matthew Bobrowski [this message]
2018-10-01 9:13 ` Amir Goldstein
2018-10-01 10:58 ` Jan Kara
2018-10-01 14:01 ` Amir Goldstein
2018-10-02 9:24 ` Jan Kara
2018-10-02 10:37 ` Amir Goldstein
2018-10-03 15:40 ` Jan Kara
2018-10-03 16:18 ` Amir Goldstein
2018-10-03 16:33 ` Jan Kara
2018-10-03 20:45 ` Matthew Bobrowski
2018-10-07 11:13 ` Matthew Bobrowski
2018-10-07 13:40 ` Amir Goldstein
2018-10-08 9:35 ` Jan Kara
2018-10-02 11:50 ` Matthew Bobrowski
2018-10-03 15:45 ` Jan Kara
2018-10-01 11:06 ` Jan Kara
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