146 lines
4.9 KiB
C++
146 lines
4.9 KiB
C++
/*
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* Copyright (C) 2012-2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <private/android_filesystem_config.h>
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#include "LogCommand.h"
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#include "LogUtils.h"
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LogCommand::LogCommand(const char* cmd) : FrameworkCommand(cmd) {
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}
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// gets a list of supplementary group IDs associated with
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// the socket peer. This is implemented by opening
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// /proc/PID/status and look for the "Group:" line.
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//
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// This function introduces races especially since status
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// can change 'shape' while reading, the net result is err
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// on lack of permission.
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//
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// Race-free alternative is to introduce pairs of sockets
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// and threads for each command and reading, one each that
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// has open permissions, and one that has restricted
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// permissions.
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static bool groupIsLog(char* buf) {
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char* ptr;
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static const char ws[] = " \n";
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for (buf = strtok_r(buf, ws, &ptr); buf; buf = strtok_r(nullptr, ws, &ptr)) {
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errno = 0;
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gid_t Gid = strtol(buf, nullptr, 10);
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if (errno != 0) {
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return false;
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}
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if (Gid == AID_LOG) {
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return true;
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}
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}
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return false;
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}
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bool clientHasLogCredentials(uid_t uid, gid_t gid, pid_t pid) {
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if ((uid == AID_ROOT) || (uid == AID_SYSTEM) || (uid == AID_LOG)) {
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return true;
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}
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if ((gid == AID_ROOT) || (gid == AID_SYSTEM) || (gid == AID_LOG)) {
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return true;
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}
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// FYI We will typically be here for 'adb logcat'
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char filename[256];
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snprintf(filename, sizeof(filename), "/proc/%u/status", pid);
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bool ret;
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bool foundLog = false;
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bool foundGid = false;
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bool foundUid = false;
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//
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// Reading /proc/<pid>/status is rife with race conditions. All of /proc
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// suffers from this and its use should be minimized. However, we have no
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// choice.
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//
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// Notably the content from one 4KB page to the next 4KB page can be from a
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// change in shape even if we are gracious enough to attempt to read
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// atomically. getline can not even guarantee a page read is not split up
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// and in effect can read from different vintages of the content.
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//
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// We are finding out in the field that a 'logcat -c' via adb occasionally
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// is returned with permission denied when we did only one pass and thus
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// breaking scripts. For security we still err on denying access if in
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// doubt, but we expect the falses should be reduced significantly as
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// three times is a charm.
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//
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for (int retry = 3; !(ret = foundGid && foundUid && foundLog) && retry;
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--retry) {
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FILE* file = fopen(filename, "r");
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if (!file) {
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continue;
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}
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char* line = nullptr;
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size_t len = 0;
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while (getline(&line, &len, file) > 0) {
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static const char groups_string[] = "Groups:\t";
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static const char uid_string[] = "Uid:\t";
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static const char gid_string[] = "Gid:\t";
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if (strncmp(groups_string, line, sizeof(groups_string) - 1) == 0) {
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if (groupIsLog(line + sizeof(groups_string) - 1)) {
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foundLog = true;
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}
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} else if (strncmp(uid_string, line, sizeof(uid_string) - 1) == 0) {
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uid_t u[4] = { (uid_t)-1, (uid_t)-1, (uid_t)-1, (uid_t)-1 };
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sscanf(line + sizeof(uid_string) - 1, "%u\t%u\t%u\t%u", &u[0],
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&u[1], &u[2], &u[3]);
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// Protect against PID reuse by checking that UID is the same
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if ((uid == u[0]) && (uid == u[1]) && (uid == u[2]) &&
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(uid == u[3])) {
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foundUid = true;
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}
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} else if (strncmp(gid_string, line, sizeof(gid_string) - 1) == 0) {
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gid_t g[4] = { (gid_t)-1, (gid_t)-1, (gid_t)-1, (gid_t)-1 };
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sscanf(line + sizeof(gid_string) - 1, "%u\t%u\t%u\t%u", &g[0],
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&g[1], &g[2], &g[3]);
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// Protect against PID reuse by checking that GID is the same
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if ((gid == g[0]) && (gid == g[1]) && (gid == g[2]) &&
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(gid == g[3])) {
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foundGid = true;
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}
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}
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}
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free(line);
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fclose(file);
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}
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return ret;
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}
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bool clientHasLogCredentials(SocketClient* cli) {
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return clientHasLogCredentials(cli->getUid(), cli->getGid(), cli->getPid());
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}
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