Messages in this thread | | | Date | Tue, 25 Mar 1997 00:34:13 +1100 (EST) | From | David Gibson <> | Subject | Re: ln weirdness |
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On Mon, 24 Mar 1997, Andrew Walker wrote:
> On Mon, 24 Mar 1997, Gerald Britton wrote: > > > as a normal user, the system lets me do this: > > > > ln /etc/shadow /tmp/testfile > > > > it then creates testfile as the same permissions and ownership of > > /etc/shadow, thus i still cannot read it, but should it really be letting > > me do this? Also, after i create the file, i cannot remove it (since i do > > not own it). Should it really be doing this? > > > > [ ... Explanation on link and t bit semantics ] > > Did that make sense? What you are experiencing is correct UNIX practice. > A lot of people who are new to UNIX (I'm not saying you're a newbie, > but you obviously weren't aware of this) don't fully grasp the permissions > stuff, and think they have discovered huge security holes in UNIX. They > haven't! Its designed that way. Its a feature not a bug.
Actually there is a security problem here (not exactly a hole, since carefully written userspace programs can avoid it) - an ordinary user can create a link to say /etc/passwd in /tmp as a name used by (for e.g.) gcc's temporary files. If root later runs gcc, it may write to this file, which will overwrite /etc/passwd. This, and a similar problem with symlinks is addressed in Andrew Tridgell's symlink patch. I'd point you to samba.anu.edu.au:/pub/linux/symlink.patch
But this seems to be an old version that addresses only the symlink, not the hard link problem.
David Gibson @ The Lorax | New from Microsoft... david%brucehall20@anu.edu.au | THNEED 95 | Which everyone, Everyone, EVERYONE needs.
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