Messages in this thread | | | Date | Wed, 17 Feb 1999 23:22:10 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: fsync on large files |
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On Thu, 18 Feb 1999, David Luyer wrote: > > If Linux ever supports hardlinked directories, I really hope there's some way > to prevent them. That's one of the reasons for the .. sanity check I thought. > > Now: > * attacker discovers a directory temporarily open (bad permissions) > * attacker hardlinks to some of the files in there > * the security checker notices the link count increase
Sure.
> The future: > * attacker discovers a directory temporarily open (bad permissions) > * attacker hardlinks to a subdirectory in it > * you need yet another security check to check the link count on directories > matches the number of real files in it, and the check has to watch for > modifications as it is checking, etc, etc
Not really.
The future: * you need another security check that checks that the link count on the directory is 1.
If you don't have a ".." entry, the link count for directories is always 1, except if you have hard links - exactly the way it works for normal files.
Note that there are many unix tools that know about the directory link counts, but they also know about ignoring it too - because there are already many filesystems that do not have the standard unix link count behaviour.
Linus
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