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/*
* 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 "LogPermissions.h"
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <vector>
#include <private/android_filesystem_config.h>
static bool checkGroup(char* buf, gid_t gidToCheck) {
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 == gidToCheck) {
return true;
}
}
return false;
}
static bool UserIsPrivileged(int id) {
return id == AID_ROOT || id == AID_SYSTEM || id == AID_LOG;
}
// 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.
static bool checkSupplementaryGroup(uid_t uid, gid_t gid, pid_t pid, gid_t gidToCheck) {
char filename[256];
snprintf(filename, sizeof(filename), "/proc/%u/status", pid);
bool ret;
bool foundGroup = 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.
//
// 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 && foundGroup) && retry; --retry) {
FILE* file = fopen(filename, "re");
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 (checkGroup(line + sizeof(groups_string) - 1, gidToCheck)) {
foundGroup = 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 clientCanWriteSecurityLog(uid_t uid, gid_t gid, pid_t pid) {
if (UserIsPrivileged(uid) || UserIsPrivileged(gid)) {
return true;
}
return checkSupplementaryGroup(uid, gid, pid, AID_SECURITY_LOG_WRITER) ||
checkSupplementaryGroup(uid, gid, pid, AID_LOG);
}
bool clientHasLogCredentials(uid_t uid, gid_t gid, pid_t pid) {
if (UserIsPrivileged(uid) || UserIsPrivileged(gid)) {
return true;
}
// FYI We will typically be here for 'adb logcat'
return checkSupplementaryGroup(uid, gid, pid, AID_LOG);
}
bool clientHasLogCredentials(SocketClient* cli) {
if (UserIsPrivileged(cli->getUid()) || UserIsPrivileged(cli->getGid())) {
return true;
}
// Kernel version 4.13 added SO_PEERGROUPS to return the supplemental groups of a peer socket,
// so try that first then fallback to the above racy checking of /proc/<pid>/status if the
// kernel is too old. Per
// https://source.android.com/devices/architecture/kernel/android-common, the fallback can be
// removed no earlier than 2024.
auto supplemental_groups = std::vector<gid_t>(16, -1);
socklen_t groups_size = supplemental_groups.size() * sizeof(gid_t);
int result = getsockopt(cli->getSocket(), SOL_SOCKET, SO_PEERGROUPS, supplemental_groups.data(),
&groups_size);
if (result != 0) {
if (errno != ERANGE) {
return clientHasLogCredentials(cli->getUid(), cli->getGid(), cli->getPid());
}
supplemental_groups.resize(groups_size / sizeof(gid_t), -1);
result = getsockopt(cli->getSocket(), SOL_SOCKET, SO_PEERGROUPS, supplemental_groups.data(),
&groups_size);
// There is still some error after resizing supplemental_groups, fallback.
if (result != 0) {
return clientHasLogCredentials(cli->getUid(), cli->getGid(), cli->getPid());
}
}
supplemental_groups.resize(groups_size / sizeof(gid_t), -1);
for (const auto& gid : supplemental_groups) {
if (UserIsPrivileged(gid)) {
return true;
}
}
return false;
}
bool clientIsExemptedFromUserConsent(SocketClient* cli) {
return cli->getUid() < AID_APP_START;
}
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