Messages in this thread |  | | Subject | Re: Security question: "Text file busy" overwriting executables but | From | (Eric W. Biederman) | Date | 05 Oct 2001 10:30:19 -0600 |
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Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
> > On Thu, 4 Oct 2001, Linus Torvalds wrote: > > > > > The reason the kernel refuses to honour it, is that MAP_DENYWRITE is an > > > excellent DoS-vehicle - you just mmap("/etc/passwd") with MAP_DENYWRITE, > > > and even root cannot write to it.. Vary nasty. > > > > <nit> > > I _really_ doubt that something does write() on /etc/passwd. Create a > > file and rename it over the thing - sure, but that's it. > > </nit> > > The MAP_DENYWRITE rule was added a long time ago because people found actual > workable DoS attacks
Do you have any details. I would like to figure out what it takes to export MAP_DENYWRITE safely to userspace.
Currently checking to see if the file is executable looks good enough. I don't see any case where this would be a problem, unless someone has set their permissions wrong.
The fix for bad permission (during a DOS attack) is either: chmod correct_permissions foo lsof foo | xargs kill or: chmod correct_permissions foo mv foo bar cp -a bar foo rm bar
Which looks fairly straight forward.
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