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SubjectRe: EUID != root + EGID = root, and CAP_SETGID
Date
Ivan Zahariev  wrote:
>Is this an intended behavior?

Yes. Setuid/setgid are a mess. For more details, you might
find the following research papers interesting:

http://www.cs.berkeley.edu/~daw/papers/setuid-usenix02.pdf
http://www.cs.berkeley.edu/~daw/papers/setuid-login08b.pdf

See, e.g., Section 5.2 of the former paper, which says:

"an effective group ID of zero does not accord any
special privileges to change groups. This is a potential
source of confusion: it is tempting to assume incorrectly
that since appropriate privileges are carried by the euid
in the setuid-like calls, they will be carried by the
egid in the setgid-like calls, but this is not how it
actually works. This misconception caused a mistake in
the manual page of setgid in Redhat Linux 7.2 (Section
6.4.1)."


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