On Tue, May 08, 2018 at 11:13:53AM -0500, hal@xxxxxxxxxxxx wrote: > > Hm, so this probably makes it possible that blockget will wander off > > into inconsistencies and fail; there's a /reason/ for the check. So > > if anything this is probably best-effort. I doubt you can rely on > > blockget even completing without error, let alone being correct. In > > that case, is it still useful to you? > > I've been testing a modified version of xfs_db on live file systems > and dirty image files, and I have yet to have blockget fail. I agree > that it's certainly possible for blockget to blow up under these > circumstances, but it's working often enough to be useful. That's a slippery slope. IMO, the only thing worse than not having a forensic tool for a specific job is having a forensic tool provided by a trusted toolkit whose results are unreliable and cannot be trusted.... > > What sort of information do you hope to gather after running > > blockget without a replay? > > Suppose I can match a string or magic number for a file of interest > at a specific byte offset in the file system image. A little arithmetic > and I have a daddr value. xfs_db let's me convert that to an fsblock > and then call blockuse -n to get the inode and file path. I've tried > it, and it works with my modifed xfs_db. There are so many ways that can go wrong on a live filesystem. Regardless of whether you've personally seen it go wrong, it's still not a reliable method of information extraction. And we know that there's every chance that xfs_db will stumble on something unexpected in a live filesystem traversal and just crash. FWIW, blockuse -n also requires a full filesystem scan to find the file path (i.e. via blockget -n). That can take a long time, affect anything that is running on the machine at the time. And by the time it's all done, there's no guarantee the path it comes up will be valid or correct.... What you are trying to do - offset/block to owner path lookups on live filesystems - is something that the FSMAP ioctl and the upcoming parent pointer functionality will solve..... > Until we get XFS support into libsleuthkit (which I'm working towards, > but it's going to be a while), having this functionality lets me > use xfs_db as a forensic tool. And it also lets me use xfs_db to > validate other forensic tools. I'd suggest, in that case, that you limit it's use to off-line or read-only snapshots of online filesystems? This would mean that the results of xfs_db operations (while eceedingly slow) will be reliable. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
