lkml.org 
[lkml]   [2003]   [Nov]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: hard links create local DoS vulnerability and security problems
Richard B. Johnson wrote:
> To prevent this, a user can set his default permissions so that
> neither group nor world can read the files. This is usually done
> by setting the attributes in the user's top directory.

Correct, but the quota problem is genuine: what if I want to create a
lot of files in /home/jamie that are readable by other users, but I
want to be able to delete them at some later time and reuse my quota
for something else?

This is quite a normal scenario on multi-user systems with quotas.

You seem to be suggesting that the only method is to have a separate
partition for each user, which is absurd.

Another method is "tree quotas" which have come up on this list
before. Hopefully they will be included one day; tree quotas seem
like they would solve this problem and some others.

> A setuid binary created with a hard-link will only work as a setuid
> binary if the directory it's in is owned by root.

That isn't true.

> If you have users that can create files or hard-links within such
> directories, you have users who either know the root password
> already or have used some exploit to become root. In any case, it's
> not a hard-link problem

/tmp is owned by root and anyone can create a hard link in /tmp to
other files, on a system where /tmp doesn't have its own filesystem.

> No. Users must be able to create hard links to files that belong
> to somebody else if they are readable. It's a requirement.

I disagree. The ability to create files and declare that someone else
can't hard link to them would be useful in a multi-user environment.

-- Jamie
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:58    [W:0.100 / U:0.912 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site