1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
|
{ config, lib, pkgs, ... }:
let
inherit (config.security) wrapperDir wrappers;
parentWrapperDir = dirOf wrapperDir;
programs =
(lib.mapAttrsToList
(n: v: (if v ? program then v else v // {program=n;}))
wrappers);
securityWrapper = pkgs.stdenv.mkDerivation {
name = "security-wrapper";
phases = [ "installPhase" "fixupPhase" ];
buildInputs = [ pkgs.libcap pkgs.libcap_ng pkgs.linuxHeaders ];
hardeningEnable = [ "pie" ];
installPhase = ''
mkdir -p $out/bin
$CC -Wall -O2 -DWRAPPER_DIR=\"${parentWrapperDir}\" \
-lcap-ng -lcap ${./wrapper.c} -o $out/bin/security-wrapper
'';
};
###### Activation script for the setcap wrappers
mkSetcapProgram =
{ program
, capabilities
, source
, owner ? "nobody"
, group ? "nogroup"
, permissions ? "u+rx,g+x,o+x"
, ...
}:
assert (lib.versionAtLeast (lib.getVersion config.boot.kernelPackages.kernel) "4.3");
''
cp ${securityWrapper}/bin/security-wrapper $wrapperDir/${program}
echo -n "${source}" > $wrapperDir/${program}.real
# Prevent races
chmod 0000 $wrapperDir/${program}
chown ${owner}.${group} $wrapperDir/${program}
# Set desired capabilities on the file plus cap_setpcap so
# the wrapper program can elevate the capabilities set on
# its file into the Ambient set.
${pkgs.libcap.out}/bin/setcap "cap_setpcap,${capabilities}" $wrapperDir/${program}
# Set the executable bit
chmod ${permissions} $wrapperDir/${program}
'';
###### Activation script for the setuid wrappers
mkSetuidProgram =
{ program
, source
, owner ? "nobody"
, group ? "nogroup"
, setuid ? false
, setgid ? false
, permissions ? "u+rx,g+x,o+x"
, ...
}:
''
cp ${securityWrapper}/bin/security-wrapper $wrapperDir/${program}
echo -n "${source}" > $wrapperDir/${program}.real
# Prevent races
chmod 0000 $wrapperDir/${program}
chown ${owner}.${group} $wrapperDir/${program}
chmod "u${if setuid then "+" else "-"}s,g${if setgid then "+" else "-"}s,${permissions}" $wrapperDir/${program}
'';
mkWrappedPrograms =
builtins.map
(s: if (s ? capabilities)
then mkSetcapProgram
({ owner = "root";
group = "root";
} // s)
else if
(s ? setuid && s.setuid) ||
(s ? setgid && s.setgid) ||
(s ? permissions)
then mkSetuidProgram s
else mkSetuidProgram
({ owner = "root";
group = "root";
setuid = true;
setgid = false;
permissions = "u+rx,g+x,o+x";
} // s)
) programs;
in
{
imports = [
(lib.mkRemovedOptionModule [ "security" "setuidOwners" ] "Use security.wrappers instead")
(lib.mkRemovedOptionModule [ "security" "setuidPrograms" ] "Use security.wrappers instead")
];
###### interface
options = {
security.wrappers = lib.mkOption {
type = lib.types.attrs;
default = {};
example = lib.literalExample
''
{ sendmail.source = "/nix/store/.../bin/sendmail";
ping = {
source = "${pkgs.iputils.out}/bin/ping";
owner = "nobody";
group = "nogroup";
capabilities = "cap_net_raw+ep";
};
}
'';
description = ''
This option allows the ownership and permissions on the setuid
wrappers for specific programs to be overridden from the
default (setuid root, but not setgid root).
<note>
<para>The sub-attribute <literal>source</literal> is mandatory,
it must be the absolute path to the program to be wrapped.
</para>
<para>The sub-attribute <literal>program</literal> is optional and
can give the wrapper program a new name. The default name is the same
as the attribute name itself.</para>
<para>Additionally, this option can set capabilities on a
wrapper program that propagates those capabilities down to the
wrapped, real program.</para>
<para>NOTE: cap_setpcap, which is required for the wrapper
program to be able to raise caps into the Ambient set is NOT
raised to the Ambient set so that the real program cannot
modify its own capabilities!! This may be too restrictive for
cases in which the real program needs cap_setpcap but it at
least leans on the side security paranoid vs. too
relaxed.</para>
</note>
'';
};
security.wrapperDir = lib.mkOption {
type = lib.types.path;
default = "/run/wrappers/bin";
internal = true;
description = ''
This option defines the path to the wrapper programs. It
should not be overriden.
'';
};
};
###### implementation
config = {
security.wrappers = {
# These are mount related wrappers that require the +s permission.
fusermount.source = "${pkgs.fuse}/bin/fusermount";
fusermount3.source = "${pkgs.fuse3}/bin/fusermount3";
mount.source = "${lib.getBin pkgs.util-linux}/bin/mount";
umount.source = "${lib.getBin pkgs.util-linux}/bin/umount";
};
boot.specialFileSystems.${parentWrapperDir} = {
fsType = "tmpfs";
options = [ "nodev" "mode=755" ];
};
# Make sure our wrapperDir exports to the PATH env variable when
# initializing the shell
environment.extraInit = ''
# Wrappers override other bin directories.
export PATH="${wrapperDir}:$PATH"
'';
###### setcap activation script
system.activationScripts.wrappers =
lib.stringAfter [ "specialfs" "users" ]
''
# Look in the system path and in the default profile for
# programs to be wrapped.
WRAPPER_PATH=${config.system.path}/bin:${config.system.path}/sbin
chmod 755 "${parentWrapperDir}"
# We want to place the tmpdirs for the wrappers to the parent dir.
wrapperDir=$(mktemp --directory --tmpdir="${parentWrapperDir}" wrappers.XXXXXXXXXX)
chmod a+rx $wrapperDir
${lib.concatStringsSep "\n" mkWrappedPrograms}
if [ -L ${wrapperDir} ]; then
# Atomically replace the symlink
# See https://axialcorps.com/2013/07/03/atomically-replacing-files-and-directories/
old=$(readlink -f ${wrapperDir})
if [ -e ${wrapperDir}-tmp ]; then
rm --force --recursive ${wrapperDir}-tmp
fi
ln --symbolic --force --no-dereference $wrapperDir ${wrapperDir}-tmp
mv --no-target-directory ${wrapperDir}-tmp ${wrapperDir}
rm --force --recursive $old
else
# For initial setup
ln --symbolic $wrapperDir ${wrapperDir}
fi
'';
};
}
|
