path watcher

[Steve Grubb]

Hello,

I had hoped some kernel guys would have jumped in here to answer...but I'll 
take a stab at it.

On Friday, August 22, 2014 04:31:24 PM John Haxby wrote:
> We have an internal group auditing updates to files but who would like
> to be able to monitor the actual modification rather than the possible
> intent to modify.

That would be a nice addition.

> The example they gave is that some program opens a file
> O_WRONLY|O_APPEND but in most cases it does not subsequently write to
> the file.  For them, the usual auditctl -p path -w wa causes lots of
> false positives.

I have asked some problematic apps to open readonly and then change flags when 
they decide they need to write. Some people comply, others can't believe I 
even asked them to do it.

> Historically, I know, that -w wa is triggered by the open(2) flags
> rather than actual modifications because "[t]he read & write syscalls
> are omitted from this set since they would overwhelm the logs."  Reading
> this again now, it looks a little specious as it seems quite easy to
> overwhelm the logs anyway.
> 
> Is there any reason why a file watcher should not use the fsnotify
> FS_ACCESS/MODIFY/ATTRIB masks before I go haring off to try to implement
> that?

I don't know the particulars. But for auditing purposes, we'd only want 1 
event no matter how many times they wrote. If the w/r flags could be cleaned up 
to be accurate and not signal just the intent, I think that would be good. 
However, I am sure there are tricky corner cases such as mmapped files that 
also need to be accounted for.

Steve