Am 25.01.2015 um 13:24 schrieb Alexander Holler: > Am 25.01.2015 um 13:08 schrieb Richard Weinberger: >> On Sun, Jan 25, 2015 at 12:42 PM, Alexander Holler <holler@xxxxxxxxxxxxx> wrote: >>> Now, after I ended up into flaming a lot (sorry again, but this topic made >>> me angry for so long and I had to spent too much time to get rid of unwanted >>> content and answering other peoples question in regard to that topic), I >>> should offer something more useful. >>> >>> So I've written down in some short words, how I think it could be done: >>> >>> First offer a syscall named sunlink() (or whatever name) which fails if it >>> can't overwrite or securely trim the contents of a file before deleting it. >>> >>> That could be done like this: >>> >>> (1) If it's a SSD or MMC without offering "Secure Trim" fail. >>> (2) If it's a plain FLASH or conventional harddisk where writing a block >>> means that block will be overwritten or if it's a SSD or MMC with "Secure >>> Trim) go on with >>> (3) Identify the blocks which contain the file contents (should be doable by >>> using the same mechanisms used to read and write a file) >>> (4) Mark the file as deleted >>> (5) Overwrite or securely trim blocks which can be deleted completely >>> (6) Build new blocks for blocks which can only partly deleted because they >>> contain information still used by the FS or other files >>> (7) Instruct the FS to us the new blocks instead of the old ones >>> (8) Overwrite or securely trim the old blocks which previously contained >>> partly information of other stuff. >>> >>> Afterwards use that new syscall in shred. >>> >>> Of course, this is just a totally simplified instruction in regard to how >>> complicated filesystems have become, but I think there isn't any black magic >>> involved in offering the user a simple way to really delete files. >> >> Or add support for the "s" chattr to major filesystems. >> > And change the manpage for the 's' attribute to change the "overwriting with zero" with some other wording. > > But thanks for the hint. I wasn't aware of that bit (maybe because it's still useless on most filesystems). > > But the above silly instruction might still help in implementing support for the 's' attribute. > > Also I wonder what happens if you delete a file with such an attribute on e.g. an SSD. I assume the user just gets a false positive that the file is deleted, which isn't much > different to what nowadays happens and doesn't therefor really help. The implementation will be challenging. Especially for modern filesytems like btrfs or f2fs which are copy-on-write based. Thanks, //richard -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
