Date: Wed, 23 Jan 2013 21:51:41 +0000 (UTC) From: jb <jb.1234abcd@gmail.com> To: freebsd-questions@freebsd.org Subject: Re: Setuid binaries and File Ownerships in FreeBSD9.0 Message-ID: <loom.20130123T224723-908@post.gmane.org> References: <201301232026.r0NKQGqF070301@x.it.okstate.edu>
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Martin McCormick <martin <at> dc.cis.okstate.edu> writes: > > The executable in question is a C program whos file > permissions are 4755 and the file belongs to root so all files > it opens are also owned by root and that works properly, but > what I need is for this application to first open a few files owned by > the caller and then later, upgrade back to root and write to > files the caller can not write to. I was hoping to avoid using > chown and chgrp and simply let the privilege level of the > application dictate ownership of any file it opens. > > When the application first runs, it gets the UID and GID > of the user and uses > > setuid(heruid); and setgid(hergid); to temporarily downgrade and > those files are owned by the right user but setuid(0); doesn't > appear to upgrade back to root. > > Is there any other strategy that gets one back to root > short of using chown and then a system call and never > downgrading privilege? > > Thank you. Unix processes have an effective (EUID, EGID), a real (UID, GID) and a saved (SUID, SGID) ID. Get familiar with this document: http://www.cs.berkeley.edu/~daw/papers/setuid-usenix02.pdf Then verify its validity on your target and current OS. jb
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