chmod failing with EPERM and PRIV_ALL needed

[David Bartley]

Hi,

I've encountered a bug in tar on OpenSolaris (possibly present in
Solaris 10 and others). I have a tarball that contains a setuid binary
(usr/bin/passwd). When I untar it as root, I see the following error:

tar: usr/bin/passwd: Cannot change mode to r-sr-sr-x: Not owner

Running this under truss we see:

2655: getppriv(PRIV_EFFECTIVE, {ffffffffffffffffffffffff}) = 0
2655:     all
2655: setppriv(PRIV_SET, PRIV_EFFECTIVE, {ffffffffffffbfffffffffff}) = 0
2655:     all,!sys_linkdir
2655: unlink("usr/bin/passwd") = 0
2655: open64("usr/bin/passwd", O_WRONLY|O_CREAT|O_EXCL, 0500) = 4
.
.
.
2655: chown("usr/bin/passwd", 0, 3) = 0
2655: chmod("usr/bin/passwd", 06555) Err#1 EPERM [ALL]

The priv calls occur in the cannot_unlink_dir function of gnulib and
disable the ability of unlink to remove a directory; the
PRIV_SYS_LINKDIR privilege is removed from the effective set. The
[ALL] part of the failed chmod means that we need PRIV_ALL (i.e. all
privileges) for this to work. Since we removed a privilege, we don't
have PRIV_ALL. I couldn't find any Solaris docs explaining why
PRIV_ALL is required so I've asked on the opensolaris mailing list for
some details [1]. Offhand, I would guess this is a security measure of
setuid root binaries.

[1] http://opensolaris.org/jive/thread.jspa?threadID=95826

-- David