1 /*
2 * Copyright (C) 2012-2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include <errno.h>
18 #include <stdio.h>
19 #include <stdlib.h>
20 #include <string.h>
21
22 #include <private/android_filesystem_config.h>
23
24 #include "LogCommand.h"
25 #include "LogUtils.h"
26
LogCommand(const char * cmd)27 LogCommand::LogCommand(const char* cmd) : FrameworkCommand(cmd) {
28 }
29
30 // gets a list of supplementary group IDs associated with
31 // the socket peer. This is implemented by opening
32 // /proc/PID/status and look for the "Group:" line.
33 //
34 // This function introduces races especially since status
35 // can change 'shape' while reading, the net result is err
36 // on lack of permission.
37 //
38 // Race-free alternative is to introduce pairs of sockets
39 // and threads for each command and reading, one each that
40 // has open permissions, and one that has restricted
41 // permissions.
42
groupIsLog(char * buf)43 static bool groupIsLog(char* buf) {
44 char* ptr;
45 static const char ws[] = " \n";
46
47 for (buf = strtok_r(buf, ws, &ptr); buf; buf = strtok_r(NULL, ws, &ptr)) {
48 errno = 0;
49 gid_t Gid = strtol(buf, NULL, 10);
50 if (errno != 0) {
51 return false;
52 }
53 if (Gid == AID_LOG) {
54 return true;
55 }
56 }
57 return false;
58 }
59
clientHasLogCredentials(uid_t uid,gid_t gid,pid_t pid)60 bool clientHasLogCredentials(uid_t uid, gid_t gid, pid_t pid) {
61 if ((uid == AID_ROOT) || (uid == AID_SYSTEM) || (uid == AID_LOG)) {
62 return true;
63 }
64
65 if ((gid == AID_ROOT) || (gid == AID_SYSTEM) || (gid == AID_LOG)) {
66 return true;
67 }
68
69 // FYI We will typically be here for 'adb logcat'
70 char filename[256];
71 snprintf(filename, sizeof(filename), "/proc/%u/status", pid);
72
73 bool ret;
74 bool foundLog = false;
75 bool foundGid = false;
76 bool foundUid = false;
77
78 //
79 // Reading /proc/<pid>/status is rife with race conditions. All of /proc
80 // suffers from this and its use should be minimized. However, we have no
81 // choice.
82 //
83 // Notably the content from one 4KB page to the next 4KB page can be from a
84 // change in shape even if we are gracious enough to attempt to read
85 // atomically. getline can not even guarantee a page read is not split up
86 // and in effect can read from different vintages of the content.
87 //
88 // We are finding out in the field that a 'logcat -c' via adb occasionally
89 // is returned with permission denied when we did only one pass and thus
90 // breaking scripts. For security we still err on denying access if in
91 // doubt, but we expect the falses should be reduced significantly as
92 // three times is a charm.
93 //
94 for (int retry = 3; !(ret = foundGid && foundUid && foundLog) && retry;
95 --retry) {
96 FILE* file = fopen(filename, "r");
97 if (!file) {
98 continue;
99 }
100
101 char* line = NULL;
102 size_t len = 0;
103 while (getline(&line, &len, file) > 0) {
104 static const char groups_string[] = "Groups:\t";
105 static const char uid_string[] = "Uid:\t";
106 static const char gid_string[] = "Gid:\t";
107
108 if (strncmp(groups_string, line, sizeof(groups_string) - 1) == 0) {
109 if (groupIsLog(line + sizeof(groups_string) - 1)) {
110 foundLog = true;
111 }
112 } else if (strncmp(uid_string, line, sizeof(uid_string) - 1) == 0) {
113 uid_t u[4] = { (uid_t)-1, (uid_t)-1, (uid_t)-1, (uid_t)-1 };
114
115 sscanf(line + sizeof(uid_string) - 1, "%u\t%u\t%u\t%u", &u[0],
116 &u[1], &u[2], &u[3]);
117
118 // Protect against PID reuse by checking that UID is the same
119 if ((uid == u[0]) && (uid == u[1]) && (uid == u[2]) &&
120 (uid == u[3])) {
121 foundUid = true;
122 }
123 } else if (strncmp(gid_string, line, sizeof(gid_string) - 1) == 0) {
124 gid_t g[4] = { (gid_t)-1, (gid_t)-1, (gid_t)-1, (gid_t)-1 };
125
126 sscanf(line + sizeof(gid_string) - 1, "%u\t%u\t%u\t%u", &g[0],
127 &g[1], &g[2], &g[3]);
128
129 // Protect against PID reuse by checking that GID is the same
130 if ((gid == g[0]) && (gid == g[1]) && (gid == g[2]) &&
131 (gid == g[3])) {
132 foundGid = true;
133 }
134 }
135 }
136 free(line);
137 fclose(file);
138 }
139
140 return ret;
141 }
142
clientHasLogCredentials(SocketClient * cli)143 bool clientHasLogCredentials(SocketClient* cli) {
144 return clientHasLogCredentials(cli->getUid(), cli->getGid(), cli->getPid());
145 }
146