cross-posted from: https://sopuli.xyz/post/12670977
iPhone owners say the latest iOS update is resurfacing deleted nudes
Nothing sinister, we just don’t delete what we say we delete. Instead we keep it in your profile to feed the algorithms and set the “deleted” flag to make you think it’s gone.
I mean, to be completely fair, that’s how data storage works.
We cannot really just make data disappear, so we let it get overwritten instead
But clearly the data is not overwritten and this was intentional. How do I know? Because that would amount to a massive amount of data, if it was de to a bug in Apple software or underlying filesystems, it would be detected in monitoring systems “Hey, we’re using 10x the data we should be, maybe we should look into it”.
The mistake was in the flag code that was supposed to fool us.
no when I say “overwritten” I mean that the area is set as deleted in the filesystem and the next time something writes to that area the data that was there before is disregarded.
the shred command in Linux tries to do this, but it may not work if the hardware moves rewritten data blocks around to mitigate wear.
shred doesn’t even necessarily work at the OS level. If you use something like ext3 and I assume ext4, normally when you overwrite data in a file, you’re not overwriting data even at the logical level in the block device. Journalling entails that you commit data to somewhere else on the disk, then update the metadata atomically to reference the new data.
It was more-practical in an era of older filesystems.
Proper deletion should include writing all ones or all zeroes to the block but y’all be lazy as fuck.
Only necessary on the ol spinning rust, with SSDs not only is it completely unnecessary, but it also burns extra writes.
Spinny’s store data magnetically on the platter with 1s and 0s, SSDs store data on the NAND as a held charge. If there’s a charge in the block it’s a 1 if there’s no charge it’s a 0.
With spinny’s, a file gets marked as “deleted” but the residual magnetic 1s and 0s will remain on the platter until eventually overwritten
With SSDs a file gets marked “deleted” and within no more than a few minutes TRIM comes along and ensures the charge on the NAND is released for that data, there’s no residuals to worry about like with spinny’s and is in fact necessary to ensure decent lifespans.
That just makes no sense to do, modern storage is write limited. As long as you used encryption the old bits mean nothing to anyone but you.
I’m not an expert, but wouldn’t proper deletion be writing random ones and zeroes to the block? Multiple times?
yeah cuz for normal, day-to-day use that’s exponentially slower the more you’re deleting
You can do that when you wipe something.
That’s skipping over the fact that recovering deleted data, even if it isn’t overwritten, is not an “oops”. It it takes extra effort, and if that data isn’t being protected it would be overwritten incidentally as drives are used.
There is a big difference in a database between “flagging” data and actually removing the association of the data to the database.
That’s how a lot of people handle deleted data in database, it’s literally just a flag. That’s why there’s a recommendation to edit Reddit posts before deleting them, to ensure they’re actually overwritten so they can’t just be restored.
Every time someone says something like this I have to explain CDC and regular old backups. There’s no way in hell Reddit doesn’t keep cold and hot backups of their shit. And while Reddit is unlikely to be doing CDC for soc2 or other compliance reasons, it’s the easiest method to capture data for analytics purposes.
CDC stands for change data capture. It’s generally done with databases by streaming the change log or ref log to a bucket or a service like Kafka where you can fast forward and rewind the log queue to see the state of the DB at any point in time. Even if you edit your comments it’s likely sitting in a Kafka topic or a snowflake bucket outside of the DB or cache used for the presentation layer.
Zero large scale websites operate with a truly single data store. There is always another layer that your user operations don’t impact
Yes, that’s certainly possible, but it’s also out of my control. I have basically three options:
- Delete account - we know this doesn’t delete comments
- Delete comment - “seems” to delete comments, but we’ve seen comments get restored - so probably using a “deleted” flag
- Edit comment with nonsense and when delete - should poison comment if they’re just using the deleted flag
That’s it. There’s no guarantee it works, but it has a much higher chance of working than the other two.
And there’s a good chance they delete old backups. Hosting every edit is expensive, so there’s a decent chance they clean up old data after some months.
Funny how you think an edit doesn’t write the old record to a comments_old table
