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/prctl.h>
18
19 #include <map>
20 #include <memory>
21
22 #include <android-base/logging.h>
23 #include <android-base/macros.h>
24
25 #define CAP_MAP_ENTRY(cap) { #cap, CAP_##cap }
26
27 namespace android {
28 namespace init {
29
30 static const std::map<std::string, int> cap_map = {
31 CAP_MAP_ENTRY(CHOWN),
32 CAP_MAP_ENTRY(DAC_OVERRIDE),
33 CAP_MAP_ENTRY(DAC_READ_SEARCH),
34 CAP_MAP_ENTRY(FOWNER),
35 CAP_MAP_ENTRY(FSETID),
36 CAP_MAP_ENTRY(KILL),
37 CAP_MAP_ENTRY(SETGID),
38 CAP_MAP_ENTRY(SETUID),
39 CAP_MAP_ENTRY(SETPCAP),
40 CAP_MAP_ENTRY(LINUX_IMMUTABLE),
41 CAP_MAP_ENTRY(NET_BIND_SERVICE),
42 CAP_MAP_ENTRY(NET_BROADCAST),
43 CAP_MAP_ENTRY(NET_ADMIN),
44 CAP_MAP_ENTRY(NET_RAW),
45 CAP_MAP_ENTRY(IPC_LOCK),
46 CAP_MAP_ENTRY(IPC_OWNER),
47 CAP_MAP_ENTRY(SYS_MODULE),
48 CAP_MAP_ENTRY(SYS_RAWIO),
49 CAP_MAP_ENTRY(SYS_CHROOT),
50 CAP_MAP_ENTRY(SYS_PTRACE),
51 CAP_MAP_ENTRY(SYS_PACCT),
52 CAP_MAP_ENTRY(SYS_ADMIN),
53 CAP_MAP_ENTRY(SYS_BOOT),
54 CAP_MAP_ENTRY(SYS_NICE),
55 CAP_MAP_ENTRY(SYS_RESOURCE),
56 CAP_MAP_ENTRY(SYS_TIME),
57 CAP_MAP_ENTRY(SYS_TTY_CONFIG),
58 CAP_MAP_ENTRY(MKNOD),
59 CAP_MAP_ENTRY(LEASE),
60 CAP_MAP_ENTRY(AUDIT_WRITE),
61 CAP_MAP_ENTRY(AUDIT_CONTROL),
62 CAP_MAP_ENTRY(SETFCAP),
63 CAP_MAP_ENTRY(MAC_OVERRIDE),
64 CAP_MAP_ENTRY(MAC_ADMIN),
65 CAP_MAP_ENTRY(SYSLOG),
66 CAP_MAP_ENTRY(WAKE_ALARM),
67 CAP_MAP_ENTRY(BLOCK_SUSPEND),
68 CAP_MAP_ENTRY(AUDIT_READ),
69 };
70
71 static_assert(CAP_LAST_CAP == CAP_AUDIT_READ, "CAP_LAST_CAP is not CAP_AUDIT_READ");
72
ComputeCapAmbientSupported()73 static bool ComputeCapAmbientSupported() {
74 #if defined(__ANDROID__)
75 return prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_CHOWN, 0, 0) >= 0;
76 #else
77 return true;
78 #endif
79 }
80
ComputeLastValidCap()81 static unsigned int ComputeLastValidCap() {
82 #if defined(__ANDROID__)
83 // Android does not support kernels < 3.8. 'CAP_WAKE_ALARM' has been present since 3.0, see
84 // http://lxr.free-electrons.com/source/include/linux/capability.h?v=3.0#L360.
85 unsigned int last_valid_cap = CAP_WAKE_ALARM;
86 for (; prctl(PR_CAPBSET_READ, last_valid_cap, 0, 0, 0) >= 0; ++last_valid_cap);
87
88 // |last_valid_cap| will be the first failing value.
89 return last_valid_cap - 1;
90 #else
91 return CAP_LAST_CAP;
92 #endif
93 }
94
DropBoundingSet(const CapSet & to_keep)95 static bool DropBoundingSet(const CapSet& to_keep) {
96 unsigned int last_valid_cap = GetLastValidCap();
97 // When dropping the bounding set, attempt to drop capabilities reported at
98 // run-time, not at compile-time.
99 // If the run-time kernel is older than the compile-time headers, this
100 // avoids dropping an invalid capability. If the run-time kernel is newer
101 // than the headers, this guarantees all capabilities (even those unknown at
102 // compile time) will be dropped.
103 for (size_t cap = 0; cap <= last_valid_cap; ++cap) {
104 if (cap < to_keep.size() && to_keep.test(cap)) {
105 // No need to drop this capability.
106 continue;
107 }
108 if (cap_drop_bound(cap) == -1) {
109 PLOG(ERROR) << "cap_drop_bound(" << cap << ") failed";
110 return false;
111 }
112 }
113 return true;
114 }
115
SetProcCaps(const CapSet & to_keep,bool add_setpcap)116 static bool SetProcCaps(const CapSet& to_keep, bool add_setpcap) {
117 ScopedCaps caps(cap_init());
118
119 cap_clear(caps.get());
120 cap_value_t value[1];
121 for (size_t cap = 0; cap < to_keep.size(); ++cap) {
122 if (to_keep.test(cap)) {
123 value[0] = cap;
124 if (cap_set_flag(caps.get(), CAP_INHERITABLE, arraysize(value), value, CAP_SET) != 0 ||
125 cap_set_flag(caps.get(), CAP_PERMITTED, arraysize(value), value, CAP_SET) != 0) {
126 PLOG(ERROR) << "cap_set_flag(INHERITABLE|PERMITTED, " << cap << ") failed";
127 return false;
128 }
129 }
130 }
131
132 if (add_setpcap) {
133 value[0] = CAP_SETPCAP;
134 if (cap_set_flag(caps.get(), CAP_PERMITTED, arraysize(value), value, CAP_SET) != 0 ||
135 cap_set_flag(caps.get(), CAP_EFFECTIVE, arraysize(value), value, CAP_SET) != 0) {
136 PLOG(ERROR) << "cap_set_flag(PERMITTED|EFFECTIVE, " << CAP_SETPCAP << ") failed";
137 return false;
138 }
139 }
140
141 if (cap_set_proc(caps.get()) != 0) {
142 PLOG(ERROR) << "cap_set_proc(" << to_keep.to_ulong() << ") failed";
143 return false;
144 }
145 return true;
146 }
147
SetAmbientCaps(const CapSet & to_raise)148 static bool SetAmbientCaps(const CapSet& to_raise) {
149 #if defined(__ANDROID__)
150 for (size_t cap = 0; cap < to_raise.size(); ++cap) {
151 if (to_raise.test(cap)) {
152 if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, cap, 0, 0) != 0) {
153 PLOG(ERROR) << "prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, " << cap << ") failed";
154 return false;
155 }
156 }
157 }
158 #endif
159 return true;
160 }
161
LookupCap(const std::string & cap_name)162 int LookupCap(const std::string& cap_name) {
163 auto e = cap_map.find(cap_name);
164 if (e != cap_map.end()) {
165 return e->second;
166 } else {
167 return -1;
168 }
169 }
170
CapAmbientSupported()171 bool CapAmbientSupported() {
172 static bool cap_ambient_supported = ComputeCapAmbientSupported();
173 return cap_ambient_supported;
174 }
175
GetLastValidCap()176 unsigned int GetLastValidCap() {
177 static unsigned int last_valid_cap = ComputeLastValidCap();
178 return last_valid_cap;
179 }
180
SetCapsForExec(const CapSet & to_keep)181 bool SetCapsForExec(const CapSet& to_keep) {
182 // Need to keep SETPCAP to drop bounding set below.
183 bool add_setpcap = true;
184 if (!SetProcCaps(to_keep, add_setpcap)) {
185 LOG(ERROR) << "failed to apply initial capset";
186 return false;
187 }
188
189 if (!DropBoundingSet(to_keep)) {
190 return false;
191 }
192
193 // If SETPCAP wasn't specifically requested, drop it now.
194 add_setpcap = false;
195 if (!SetProcCaps(to_keep, add_setpcap)) {
196 LOG(ERROR) << "failed to apply final capset";
197 return false;
198 }
199
200 // Add the capabilities to the ambient set so that they are preserved across
201 // execve(2).
202 // See http://man7.org/linux/man-pages/man7/capabilities.7.html.
203 return SetAmbientCaps(to_keep);
204 }
205
DropInheritableCaps()206 bool DropInheritableCaps() {
207 ScopedCaps caps(cap_get_proc());
208 if (cap_clear_flag(caps.get(), CAP_INHERITABLE) == -1) {
209 PLOG(ERROR) << "cap_clear_flag(INHERITABLE) failed";
210 return false;
211 }
212 if (cap_set_proc(caps.get()) != 0) {
213 PLOG(ERROR) << "cap_set_proc() failed";
214 return false;
215 }
216 return true;
217 }
218
219 } // namespace init
220 } // namespace android
221