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Subject: [Bug 220779] getgroups result is affected by setegid
Date: Wed, 04 Oct 2017 20:33:16 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D220779

paulm <paulm@tetrardus.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paulm@tetrardus.net

--- Comment #5 from paulm <paulm@tetrardus.net> ---
The effective GID is stored in cr_groups[0] in the ucred struct.

kern_setgroups() writes to cr_groups[0] in the ucred struct.

Therefore, the syscall setgroups(int ngroups, const gid_t *gidset) overwrit=
es
the effective GID at cr_groups[0] with the first GID in *gidset.

(Because setgroups() writes to cr_groups[0], a subsequent call to setegid()
will overwrite the supplementary GID at that location.  I think this is the
symptom Michael Zuo is calling attention to.)=20=20=20=20=20=20

Unless I'm confused about something, the implementation of setgroups() shou=
ld
write the supplementary group list starting at an offset of +1 in the cr_gr=
oups
array in struct ucred in order to preserve the effective GID at cr_groups[0=
].

--=20
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