Messages in this thread | | | Date | Sun, 12 May 2002 11:37:30 -0700 | Subject | Re: [RFC] ext2 and ext3 block reservations can be bypassed | From | Elladan <> |
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On Sun, May 12, 2002 at 02:15:12PM -0400, Alexander Viro wrote: > > On Sun, 12 May 2002, Elladan wrote: > > > > It just happens that the suid program wasn't the one who chose what file > > it was going to write stdout to - the shell did. > > > > Thus, the security violation. > > <shrug> relying on 5% in security-sensitive setup is *dumb*. > In that case you need properly set quota (better yet, no lusers with write > access anywhere on that fs).. > > There are worse holes problems 5% rule. E.g. you can create a > file with hole, mmap over that hole, dirty the pages and exit. Guess > who ends up writing them out? Right, kswapd. Which is run as root. > No suid applications required...
Regardless of whether it's a good thing to depend on security-wise, it is a problem to have something that appears to be a security feature which doesn't actually work.
Reading the documentation, I would expect that if I create an ext3 filesystem, reserve 20% of it for root, and then run a cron job as root that uses 16% of that filesystem periodically, that cron job will not actually fail whenever some luser decides they want it to.
I don't recall seeing it plastered in huge letters, "This space reserve is just a convenience feature, and can easily be circumvented by the user. You must never rely on it for anything."
Having unsupported security features is typically a bad idea.
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