Re: [patch] fanotify: Document FAN_OPEN_EXEC and FAN_OPEN_EXEC_PERM

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Hi Michael,

On Tue, Feb 26, 2019 at 04:43:01PM +0100, Michael Kerrisk (man-pages) wrote:
> Hello Matthew,
> 
> On 1/12/19 2:56 AM, Matthew Bobrowski wrote:
> > New event masks have been added to the fanotify API. Documentation to
> > support the use and behaviour of these new masks has been added
> > accordingly.
> >
> > Signed-off-by: Matthew Bobrowski <mbobrowski@xxxxxxxxxxxxxx>
> > Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
> 
> Thanks for the patch. I've applied, but I have a question below.

Sure, response to your question is inline below.

> > ---
> >  man2/fanotify_mark.2 | 60 ++++++++++++++++++++++++++++++++++++++++++++
> >  man7/fanotify.7      | 18 +++++++++++++
> >  2 files changed, 78 insertions(+)
> > 
> > diff --git a/man2/fanotify_mark.2 b/man2/fanotify_mark.2
> > index a9a482fe7..613c86cc4 100644
> > --- a/man2/fanotify_mark.2
> > +++ b/man2/fanotify_mark.2
> > @@ -149,6 +149,12 @@ Create an event when a read-only file or directory is closed.
> >  .B FAN_OPEN
> >  Create an event when a file or directory is opened.
> >  .TP
> > +.B FAN_OPEN_EXEC
> > +Create an event when a file is opened with the intent to be executed.
> > +See
> > +.B NOTES
> > +for additional details.
> > +.TP
> >  .B FAN_Q_OVERFLOW
> >  Create an event when an overflow of the event queue occurs.
> >  The size of the event queue is limited to 16384 entries if
> > @@ -164,6 +170,18 @@ or
> >  .B FAN_CLASS_CONTENT
> >  is required.
> >  .TP
> > +.B FAN_OPEN_EXEC_PERM
> > +Create an event when a permission to open a file for execution is
> > +requested.
> > +An fanotify file descriptor created with
> > +.B FAN_CLASS_PRE_CONTENT
> > +or
> > +.B FAN_CLASS_CONTENT
> > +is required.
> > +See
> > +.B NOTES
> > +for additional details.
> > +.TP
> >  .B FAN_ACCESS_PERM
> >  Create an event when a permission to read a file or directory is requested.
> >  An fanotify file descriptor created with
> > @@ -309,6 +327,48 @@ was introduced in version 2.6.36 of the Linux kernel and enabled in version
> >  2.6.37.
> >  .SH CONFORMING TO
> >  This system call is Linux-specific.
> > +.SH NOTES
> > +When using either
> > +.B FAN_OPEN_EXEC
> > +or
> > +.B FAN_OPEN_EXEC_PERM
> > +within the
> > +.IR mask ,
> > +events of these types will only be returned when the direct execution of a
> > +program occurs.
> > +More specifically, this means that events of these types shall be generated
> > +for files that are opened using system calls
> > +.BR execve(2) ,
> > +.BR execveat(2) ,
> > +or
> > +.BR uselib(2) .
> > +Events of these types will not be raised in the situation where an
> > +interpreter reads data as input and subsequently results in arbitrary
> > +computation.
> 
> This last sentence is not so clear to me. Are you here talking about
> the situation where (say) awk(1) reads a script file and interprets
> its contents?

That's correct. Another very similar situation would be where Python is passed
a file for interpretation.

-- 
Matthew Bobrowski



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