1 // Copyright (C) 2016 The Android Open Source Project
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include "capabilities.h"
16
17 #include <sys/capability.h>
18 #include <sys/prctl.h>
19
20 #include <map>
21 #include <memory>
22
23 #include <android-base/logging.h>
24 #include <android-base/macros.h>
25
26 #define CAP_MAP_ENTRY(cap) { #cap, CAP_##cap }
27
28 namespace android {
29 namespace init {
30
31 static const std::map<std::string, int> cap_map = {
32 CAP_MAP_ENTRY(CHOWN),
33 CAP_MAP_ENTRY(DAC_OVERRIDE),
34 CAP_MAP_ENTRY(DAC_READ_SEARCH),
35 CAP_MAP_ENTRY(FOWNER),
36 CAP_MAP_ENTRY(FSETID),
37 CAP_MAP_ENTRY(KILL),
38 CAP_MAP_ENTRY(SETGID),
39 CAP_MAP_ENTRY(SETUID),
40 CAP_MAP_ENTRY(SETPCAP),
41 CAP_MAP_ENTRY(LINUX_IMMUTABLE),
42 CAP_MAP_ENTRY(NET_BIND_SERVICE),
43 CAP_MAP_ENTRY(NET_BROADCAST),
44 CAP_MAP_ENTRY(NET_ADMIN),
45 CAP_MAP_ENTRY(NET_RAW),
46 CAP_MAP_ENTRY(IPC_LOCK),
47 CAP_MAP_ENTRY(IPC_OWNER),
48 CAP_MAP_ENTRY(SYS_MODULE),
49 CAP_MAP_ENTRY(SYS_RAWIO),
50 CAP_MAP_ENTRY(SYS_CHROOT),
51 CAP_MAP_ENTRY(SYS_PTRACE),
52 CAP_MAP_ENTRY(SYS_PACCT),
53 CAP_MAP_ENTRY(SYS_ADMIN),
54 CAP_MAP_ENTRY(SYS_BOOT),
55 CAP_MAP_ENTRY(SYS_NICE),
56 CAP_MAP_ENTRY(SYS_RESOURCE),
57 CAP_MAP_ENTRY(SYS_TIME),
58 CAP_MAP_ENTRY(SYS_TTY_CONFIG),
59 CAP_MAP_ENTRY(MKNOD),
60 CAP_MAP_ENTRY(LEASE),
61 CAP_MAP_ENTRY(AUDIT_WRITE),
62 CAP_MAP_ENTRY(AUDIT_CONTROL),
63 CAP_MAP_ENTRY(SETFCAP),
64 CAP_MAP_ENTRY(MAC_OVERRIDE),
65 CAP_MAP_ENTRY(MAC_ADMIN),
66 CAP_MAP_ENTRY(SYSLOG),
67 CAP_MAP_ENTRY(WAKE_ALARM),
68 CAP_MAP_ENTRY(BLOCK_SUSPEND),
69 CAP_MAP_ENTRY(AUDIT_READ),
70 };
71
72 static_assert(CAP_LAST_CAP == CAP_AUDIT_READ, "CAP_LAST_CAP is not CAP_AUDIT_READ");
73
ComputeCapAmbientSupported()74 static bool ComputeCapAmbientSupported() {
75 return prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_CHOWN, 0, 0) >= 0;
76 }
77
ComputeLastValidCap()78 static unsigned int ComputeLastValidCap() {
79 // Android does not support kernels < 3.8. 'CAP_WAKE_ALARM' has been present since 3.0, see
80 // http://lxr.free-electrons.com/source/include/linux/capability.h?v=3.0#L360.
81 unsigned int last_valid_cap = CAP_WAKE_ALARM;
82 for (; prctl(PR_CAPBSET_READ, last_valid_cap, 0, 0, 0) >= 0; ++last_valid_cap);
83
84 // |last_valid_cap| will be the first failing value.
85 return last_valid_cap - 1;
86 }
87
DropBoundingSet(const CapSet & to_keep)88 static bool DropBoundingSet(const CapSet& to_keep) {
89 unsigned int last_valid_cap = GetLastValidCap();
90 // When dropping the bounding set, attempt to drop capabilities reported at
91 // run-time, not at compile-time.
92 // If the run-time kernel is older than the compile-time headers, this
93 // avoids dropping an invalid capability. If the run-time kernel is newer
94 // than the headers, this guarantees all capabilities (even those unknown at
95 // compile time) will be dropped.
96 for (size_t cap = 0; cap <= last_valid_cap; ++cap) {
97 if (cap < to_keep.size() && to_keep.test(cap)) {
98 // No need to drop this capability.
99 continue;
100 }
101 if (cap_drop_bound(cap) == -1) {
102 PLOG(ERROR) << "cap_drop_bound(" << cap << ") failed";
103 return false;
104 }
105 }
106 return true;
107 }
108
SetProcCaps(const CapSet & to_keep,bool add_setpcap)109 static bool SetProcCaps(const CapSet& to_keep, bool add_setpcap) {
110 ScopedCaps caps(cap_init());
111
112 cap_clear(caps.get());
113 cap_value_t value[1];
114 for (size_t cap = 0; cap < to_keep.size(); ++cap) {
115 if (to_keep.test(cap)) {
116 value[0] = cap;
117 if (cap_set_flag(caps.get(), CAP_INHERITABLE, arraysize(value), value, CAP_SET) != 0 ||
118 cap_set_flag(caps.get(), CAP_PERMITTED, arraysize(value), value, CAP_SET) != 0) {
119 PLOG(ERROR) << "cap_set_flag(INHERITABLE|PERMITTED, " << cap << ") failed";
120 return false;
121 }
122 }
123 }
124
125 if (add_setpcap) {
126 value[0] = CAP_SETPCAP;
127 if (cap_set_flag(caps.get(), CAP_PERMITTED, arraysize(value), value, CAP_SET) != 0 ||
128 cap_set_flag(caps.get(), CAP_EFFECTIVE, arraysize(value), value, CAP_SET) != 0) {
129 PLOG(ERROR) << "cap_set_flag(PERMITTED|EFFECTIVE, " << CAP_SETPCAP << ") failed";
130 return false;
131 }
132 }
133
134 if (cap_set_proc(caps.get()) != 0) {
135 PLOG(ERROR) << "cap_set_proc(" << to_keep.to_ulong() << ") failed";
136 return false;
137 }
138 return true;
139 }
140
SetAmbientCaps(const CapSet & to_raise)141 static bool SetAmbientCaps(const CapSet& to_raise) {
142 for (size_t cap = 0; cap < to_raise.size(); ++cap) {
143 if (to_raise.test(cap)) {
144 if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, cap, 0, 0) != 0) {
145 PLOG(ERROR) << "prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, " << cap << ") failed";
146 return false;
147 }
148 }
149 }
150 return true;
151 }
152
LookupCap(const std::string & cap_name)153 int LookupCap(const std::string& cap_name) {
154 auto e = cap_map.find(cap_name);
155 if (e != cap_map.end()) {
156 return e->second;
157 } else {
158 return -1;
159 }
160 }
161
CapAmbientSupported()162 bool CapAmbientSupported() {
163 static bool cap_ambient_supported = ComputeCapAmbientSupported();
164 return cap_ambient_supported;
165 }
166
GetLastValidCap()167 unsigned int GetLastValidCap() {
168 static unsigned int last_valid_cap = ComputeLastValidCap();
169 return last_valid_cap;
170 }
171
SetCapsForExec(const CapSet & to_keep)172 bool SetCapsForExec(const CapSet& to_keep) {
173 // Need to keep SETPCAP to drop bounding set below.
174 bool add_setpcap = true;
175 if (!SetProcCaps(to_keep, add_setpcap)) {
176 LOG(ERROR) << "failed to apply initial capset";
177 return false;
178 }
179
180 if (!DropBoundingSet(to_keep)) {
181 return false;
182 }
183
184 // If SETPCAP wasn't specifically requested, drop it now.
185 add_setpcap = false;
186 if (!SetProcCaps(to_keep, add_setpcap)) {
187 LOG(ERROR) << "failed to apply final capset";
188 return false;
189 }
190
191 // Add the capabilities to the ambient set so that they are preserved across
192 // execve(2).
193 // See http://man7.org/linux/man-pages/man7/capabilities.7.html.
194 return SetAmbientCaps(to_keep);
195 }
196
197 } // namespace init
198 } // namespace android
199