All, I am interested in any Linux based capability that will monitor identified files and report on actual changes to the monitored file. I know there are methods of recording that the file has been changed (e.g. aide and/or monitor writes via auditd), but I want to know what has changed ... basically something that would provide a 'diff' like output. Now there are tools like Samhain that will record the content changes of a file that is <= 92000 bytes in size, but I am interested in a more lightweight solution ... perhaps a simple inotify(7) based utility that perhaps maintains a copy of the file(s) in core (in compressed format) and based on inotify() returns checks for changes and reports (somehow yet to be defined) the before/after changes. Is there anything 'out there' that list members are aware of? If not, would the following utility be of interest? On startup, load the monitored file(s) (saving a compressed copy in memory). Then, using inotify, monitor for changes and if so, emit some kind of record defining the change and change the compressed in-memory copy. If so, is our mailing list and the contributed portion of auditd an appropriate repository for such a tool. Naturally, such a tool would be supported by appropriate auditd monitoring that will take care of changing file attributes etc and file writes. That is, auditd tells me who and the utility tells me what. Regards Burn -- Linux-audit mailing list Linux-audit(a)redhat.com https://www.redhat.com/mailman/listinfo/linux-audit

I am interested in any Linux based capability that will monitor identified files and report on actual changes to the monitored file.

I know there are methods of recording that the file has been changed (e.g. aide and/or monitor writes via auditd), but I want to know what has changed ... basically something that would provide a 'diff' like output. Now there are tools like Samhain that will record the content changes of a file that is <= 92000 bytes in size, but I am interested in a more lightweight solution ... perhaps a simple inotify(7) based utility that perhaps maintains a copy of the file(s) in core (in compressed format) and based on inotify() returns checks for changes and reports (somehow yet to be defined) the before/after changes.

Is there anything 'out there' that list members are aware of? If not, would the following utility be of interest?

On startup, load the monitored file(s) (saving a compressed copy in memory). Then, using inotify, monitor for changes and if so, emit some kind of record defining the change and change the compressed in-memory copy. If so, is our mailing list and the contributed portion of auditd an appropriate repository for such a tool.

Naturally, such a tool would be supported by appropriate auditd monitoring that will take care of changing file attributes etc and file writes. That is, auditd tells me who and the utility tells me what.

Not to hijack your thread here, but as long as there might be development in the area of auditing changes to file with aide (sounds like maybe it would be an aide plugin), I would suggest it would also be very nice to know the names of files being copied/burned to removable media. I don't know how one would accomplish this though. Kevin -----Original Message----- From: linux-audit-bounces(a)redhat.com [mailto:linux-audit-bounces@redhat.com] On Behalf Of Steve Grubb Sent: Monday, July 20, 2015 7:08 PM To: linux-audit(a)redhat.com; burn(a)swtf.dyndns.org Subject: EXT :Re: Configuration file monitoring - reporting content changes On Monday, July 20, 2015 09:53:47 PM Burn Alting wrote: > I am interested in any Linux based capability that will monitor > identified files and report on actual changes to the monitored file. I know of nothing that does this. But as long as the list of files is limited, it doesn't sound like a hard program to write. > I know there are methods of recording that the file has been changed (e.g. > aide and/or monitor writes via auditd), but I want to know what has > changed ... basically something that would provide a 'diff' like output. > > Now there are tools like Samhain that will record the content changes > of a file that is <= 92000 bytes in size, but I am interested in a > more lightweight solution ... perhaps a simple inotify(7) based > utility that perhaps maintains a copy of the file(s) in core (in > compressed format) and based on inotify() returns checks for changes > and reports (somehow yet to be defined) the before/after changes. It would have to be after the changes since inotify would tell you something happened. > Is there anything 'out there' that list members are aware of? > > If not, would the following utility be of interest? I am certain there are people that are interested in this even if no one is speaking up on it. > On startup, load the monitored file(s) (saving a compressed copy in memory). > Then, using inotify, monitor for changes and if so, emit some kind of record > defining the change and change the compressed in-memory copy. If so, is > our mailing list and the contributed portion of auditd an appropriate > repository for such a tool. That's an interesting question. > Naturally, such a tool would be supported by appropriate auditd > monitoring that will take care of changing file attributes etc and file > writes. That is, auditd tells me who and the utility tells me what. Correlating the changes might be interesting. There can be a long time between opening a file and closing it. The inotify might trigger on the changes during flushing to disk. Or what if the file was mmap'ed? I don't know if that would be caught. But there's only 1 way to find out. :-) Like I said, I think its a straight forward program to write. No one's specifically asked for this. But we tap dance around the subject by patching programs to record what is being changed (shadow-utils). So, there is a precedence that this is needed. But Common Criteria makes it only for trusted databases. One file you would exempt, I presume, is /etc/shadow and /etc/gshadow. Any one else with an opinion? -Steve -- Linux-audit mailing list Linux-audit(a)redhat.com https://www.redhat.com/mailman/listinfo/linux-audit

On 07/20/2015 07:08 PM, Steve Grubb wrote: > On Monday, July 20, 2015 09:53:47 PM Burn Alting wrote: >> I am interested in any Linux based capability that will monitor >> identified files and report on actual changes to the monitored file. > > I know of nothing that does this. But as long as the list of files is > limited, it doesn't sound like a hard program to write. > > Any one else with an opinion? Yes :-) I'm not so sure it's an easy program to write and be robust in a variety of scenarios. I know because I wrote such a program once. The basic problem is most people think in terms of monitoring a file by name (e.g. it's pathname). But inotify operates on inodes, not filenames. If that file is subject to any variety of log rotation strategies or modifications by a configuration manager whereby the file is renamed or moved to a different directory then any program using inotify to monitor the file needs to become reasonably sophisticated and be able to track those changes. It is entirely possible for two processes to have opened the same file by name but have them be 2 different files (e.g. after opening the file path is modified but the process still has the original inode open, now a 2nd process opens the same filename but gets a different inode). Conflating inodes with filenames can lead to unexpected results and if the purpose is some sort of security monitoring it will be important these issues are accounted for.

Some of this is discussed in these documents which accompany the lwatch (Log Watch) program I wrote: https://jdennis.fedorapeople.org/lwatch/html/InotifyOverview.html https://jdennis.fedorapeople.org/lwatch/html/LogWatchOverview.html