summaryrefslogtreecommitdiffstats
blob: 8bff9da46d2e6c0801510d27537cab1a0714f265 (plain) (blame)
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
/*
 * Copyright (C) 2012-2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <private/android_filesystem_config.h>

#include "LogCommand.h"
#include "LogUtils.h"

LogCommand::LogCommand(const char* cmd) : FrameworkCommand(cmd) {
}

// gets a list of supplementary group IDs associated with
// the socket peer.  This is implemented by opening
// /proc/PID/status and look for the "Group:" line.
//
// This function introduces races especially since status
// can change 'shape' while reading, the net result is err
// on lack of permission.
//
// Race-free alternative is to introduce pairs of sockets
// and threads for each command and reading, one each that
// has open permissions, and one that has restricted
// permissions.

static bool groupIsLog(char* buf) {
    char* ptr;
    static const char ws[] = " \n";

    for (buf = strtok_r(buf, ws, &ptr); buf; buf = strtok_r(nullptr, ws, &ptr)) {
        errno = 0;
        gid_t Gid = strtol(buf, nullptr, 10);
        if (errno != 0) {
            return false;
        }
        if (Gid == AID_LOG) {
            return true;
        }
    }
    return false;
}

bool clientHasLogCredentials(uid_t uid, gid_t gid, pid_t pid) {
    if ((uid == AID_ROOT) || (uid == AID_SYSTEM) || (uid == AID_LOG)) {
        return true;
    }

    if ((gid == AID_ROOT) || (gid == AID_SYSTEM) || (gid == AID_LOG)) {
        return true;
    }

    // FYI We will typically be here for 'adb logcat'
    char filename[256];
    snprintf(filename, sizeof(filename), "/proc/%u/status", pid);

    bool ret;
    bool foundLog = false;
    bool foundGid = false;
    bool foundUid = false;

    //
    // Reading /proc/<pid>/status is rife with race conditions. All of /proc
    // suffers from this and its use should be minimized. However, we have no
    // choice.
    //
    // Notably the content from one 4KB page to the next 4KB page can be from a
    // change in shape even if we are gracious enough to attempt to read
    // atomically. getline can not even guarantee a page read is not split up
    // and in effect can read from different vintages of the content.
    //
    // We are finding out in the field that a 'logcat -c' via adb occasionally
    // is returned with permission denied when we did only one pass and thus
    // breaking scripts. For security we still err on denying access if in
    // doubt, but we expect the falses  should be reduced significantly as
    // three times is a charm.
    //
    for (int retry = 3; !(ret = foundGid && foundUid && foundLog) && retry;
         --retry) {
        FILE* file = fopen(filename, "r");
        if (!file) {
            continue;
        }

        char* line = nullptr;
        size_t len = 0;
        while (getline(&line, &len, file) > 0) {
            static const char groups_string[] = "Groups:\t";
            static const char uid_string[] = "Uid:\t";
            static const char gid_string[] = "Gid:\t";

            if (strncmp(groups_string, line, sizeof(groups_string) - 1) == 0) {
                if (groupIsLog(line + sizeof(groups_string) - 1)) {
                    foundLog = true;
                }
            } else if (strncmp(uid_string, line, sizeof(uid_string) - 1) == 0) {
                uid_t u[4] = { (uid_t)-1, (uid_t)-1, (uid_t)-1, (uid_t)-1 };

                sscanf(line + sizeof(uid_string) - 1, "%u\t%u\t%u\t%u", &u[0],
                       &u[1], &u[2], &u[3]);

                // Protect against PID reuse by checking that UID is the same
                if ((uid == u[0]) && (uid == u[1]) && (uid == u[2]) &&
                    (uid == u[3])) {
                    foundUid = true;
                }
            } else if (strncmp(gid_string, line, sizeof(gid_string) - 1) == 0) {
                gid_t g[4] = { (gid_t)-1, (gid_t)-1, (gid_t)-1, (gid_t)-1 };

                sscanf(line + sizeof(gid_string) - 1, "%u\t%u\t%u\t%u", &g[0],
                       &g[1], &g[2], &g[3]);

                // Protect against PID reuse by checking that GID is the same
                if ((gid == g[0]) && (gid == g[1]) && (gid == g[2]) &&
                    (gid == g[3])) {
                    foundGid = true;
                }
            }
        }
        free(line);
        fclose(file);
    }

    return ret;
}

bool clientHasLogCredentials(SocketClient* cli) {
    return clientHasLogCredentials(cli->getUid(), cli->getGid(), cli->getPid());
}