BetterAuthorizationSampleLibInstallTool.c

/*
    File:       BetterAuthorizationSampleLibInstallTool.c
 
    Contains:   Tool to install BetterAuthorizationSampleLib-based privileged helper tools.
 
    Written by: DTS
 
    Copyright:  Copyright (c) 2007 Apple Inc. All Rights Reserved.
 
    Disclaimer: IMPORTANT:  This Apple software is supplied to you by Apple, Inc.
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                IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR
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 */
 
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdbool.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <sys/stat.h>
 
// Allows access to path information associated with tool and plist installation
// from BetterAuthorizationSampleLib.h
#define BAS_PRIVATE 1       
 
#include "BetterAuthorizationSampleLib.h"
 
extern char **environ;
 
static int RunLaunchCtl(
    bool                        junkStdIO, 
    const char                  *command, 
    const char                  *plistPath
)
    // Handles all the invocations of launchctl by doing the fork() + execve()
    // for proper clean-up. Only two commands are really supported by our
    // implementation; loading and unloading of a job via the plist pointed at 
    // (const char *) plistPath.
{   
    int             err;
    const char *    args[5];
    pid_t           childPID;
    pid_t           waitResult;
    int             status;
    
    // Pre-conditions.
    assert(command != NULL);
    assert(plistPath != NULL);
    
    // Make sure we get sensible logging even if we never get to the waitpid.
    
    status = 0;
    
    // Set up the launchctl arguments.  We run launchctl using StartupItemContext 
    // because, in future system software, launchctl may decide on the launchd 
    // to talk to based on your Mach bootstrap namespace rather than your RUID.
    
    args[0] = "/bin/launchctl";
    args[1] = command;              // "load" or "unload"
    args[2] = "-w";
    args[3] = plistPath;            // path to plist
    args[4] = NULL;
 
    fprintf(stderr, "launchctl %s %s '%s'\n", args[1], args[2], args[3]);
    
    // Do the standard fork/exec dance.
    
    childPID = fork();
    switch (childPID) {
        case 0:
            // child
            err = 0;
            
            // If we've been told to junk the I/O for launchctl, open 
            // /dev/null and dup that down to stdin, stdout, and stderr.
            
            if (junkStdIO) {
                int     fd;
                int     err2;
 
                fd = open("/dev/null", O_RDWR);
                if (fd < 0) {
                    err = errno;
                }
                if (err == 0) {
                    if ( dup2(fd, STDIN_FILENO) < 0 ) {
                        err = errno;
                    }
                }
                if (err == 0) {
                    if ( dup2(fd, STDOUT_FILENO) < 0 ) {
                        err = errno;
                    }
                }
                if (err == 0) {
                    if ( dup2(fd, STDERR_FILENO) < 0 ) {
                        err = errno;
                    }
                }
                err2 = close(fd);
                if (err2 < 0) {
                    err2 = 0;
                }
                if (err == 0) {
                    err = err2;
                }
            }
            if (err == 0) {
                err = execve(args[0], (char **) args, environ);
            }
            if (err < 0) {
                err = errno;
            }
            _exit(EXIT_FAILURE);
            break;
        case -1:
            err = errno;
            break;
        default:
            err = 0;
            break;
    }
    
    // Only the parent gets here.  Wait for the child to complete and get its 
    // exit status.
    
    if (err == 0) {
        do {
            waitResult = waitpid(childPID, &status, 0);
        } while ( (waitResult == -1) && (errno == EINTR) );
 
        if (waitResult < 0) {
            err = errno;
        } else {
            assert(waitResult == childPID);
 
            if ( ! WIFEXITED(status) || (WEXITSTATUS(status) != 0) ) {
                err = EINVAL;
            }
        }
    }
 
    fprintf(stderr, "launchctl -> %d %ld 0x%x\n", err, (long) childPID, status);
    
    return err;
}
 
static int CopyFileOverwriting(
    const char                  *sourcePath, 
    mode_t                      destMode, 
    const char                  *destPath
)
    // Our own version of a file copy. This routine will either handle
    // the copy of the tool binary or the plist file associated with
    // that binary. As the function name suggests, it writes over any 
    // existing file pointed to by (const char *) destPath.
{
    int         err;
    int         junk;
    int         sourceFD;
    int         destFD;
    char        buf[65536];
    
    // Pre-conditions.
    assert(sourcePath != NULL);
    assert(destPath != NULL);
    
    (void) unlink(destPath);
    
    destFD = -1;
    
    err = 0;
    sourceFD = open(sourcePath, O_RDONLY);
    if (sourceFD < 0) {
        err = errno;
    }
    
    if (err == 0) {
        destFD = open(destPath, O_CREAT | O_EXCL | O_WRONLY, destMode);
        if (destFD < 0) {
            err = errno;
        }
    }
    
    if (err == 0) {
        ssize_t bytesReadThisTime;
        ssize_t bytesWrittenThisTime;
        ssize_t bytesWritten;
        
        do {
            bytesReadThisTime = read(sourceFD, buf, sizeof(buf));
            if (bytesReadThisTime < 0) {
                err = errno;
            }
            
            bytesWritten = 0;
            while ( (err == 0) && (bytesWritten < bytesReadThisTime) ) {
                bytesWrittenThisTime = write(destFD, &buf[bytesWritten], bytesReadThisTime - bytesWritten);
                if (bytesWrittenThisTime < 0) {
                    err = errno;
                } else {
                    bytesWritten += bytesWrittenThisTime;
                }
            }
 
        } while ( (err == 0) && (bytesReadThisTime != 0) );
    }
    
    // Clean up.
    
    if (sourceFD != -1) {
        junk = close(sourceFD);
        assert(junk == 0);
    }
    if (destFD != -1) {
        junk = close(destFD);
        assert(junk == 0);
    }
 
    fprintf(stderr, "copy '%s' %#o '%s' -> %d\n", sourcePath, (int) destMode, destPath, err);
    
    return err;
}
 
static int InstallCommand(
    const char *                bundleID, 
    const char *                toolSourcePath, 
    const char *                plistSourcePath
)
    // Heavy lifting function for handling all the necessary steps to install a
    // helper tool in the correct location, with the correct permissions,
    // and call launchctl in order to load it as a current job.
{
    int         err;
    char        toolDestPath[PATH_MAX];
    char        plistDestPath[PATH_MAX];
    struct stat sb;
    static const mode_t kDirectoryMode  = ACCESSPERMS & ~(S_IWGRP | S_IWOTH);
    static const mode_t kExecutableMode = ACCESSPERMS & ~(S_IWGRP | S_IWOTH);
    static const mode_t kFileMode       = DEFFILEMODE & ~(S_IWGRP | S_IWOTH);
    
    // Pre-conditions.
    assert(bundleID != NULL);
    assert(toolSourcePath != NULL);
    assert(plistSourcePath != NULL);
    
    (void) snprintf(toolDestPath,  sizeof(toolDestPath),  kBASToolPathFormat,  bundleID);
    (void) snprintf(plistDestPath, sizeof(plistDestPath), kBASPlistPathFormat, bundleID);
 
    // Stop the helper tool if it's currently running.
 
    (void) RunLaunchCtl(true, "unload", plistDestPath);
 
    // Create the PrivilegedHelperTools directory.  The owner will be "root" because 
    // we're running as root (our EUID is 0).  The group will be "admin" because 
    // it's inherited from "/Library".  The permissions will be rwxr-xr-x because 
    // of kDirectoryMode combined with our umask.
 
    err = mkdir(kBASToolDirPath, kDirectoryMode);
    if (err < 0) {
        err = errno;
    }
    fprintf(stderr, "mkdir '%s' %#o -> %d\n", kBASToolDirPath, kDirectoryMode, err);
    if ( (err == 0) || (err == EEXIST) ) {
        err = stat(kBASToolDirPath, &sb);
        if (err < 0) {
            err = errno;
        }
    }
    
    // /Library/PrivilegedHelperTools may have come from a number of places:
    //
    // A. We may have just created it.  In this case it will be 
    //    root:admin rwxr-xr-x.
    //
    // B. It may have been correctly created by someone else.  By definition, 
    //    that makes it root:wheel rwxr-xr-x.
    //
    // C. It may have been created (or moved here) incorrectly (or maliciously) 
    //    by someone else.  In that case it will be u:g xxxxxxxxx, where u is 
    //    not root, or root:g xxxxwxxwx (that is, root-owned by writeable by 
    //    someone other than root).
    //
    // In case A, we want to correct the group.  In case B, we want to do 
    // nothing.  In case C, we want to fail.
 
    if (err == 0) {
        if ( (sb.st_uid == 0) && (sb.st_gid == 0) ) {
            // case B -- do nothing
        } else if ( (sb.st_uid == 0) && (sb.st_gid != 0) && ((sb.st_mode & ALLPERMS) == kDirectoryMode) ) {
            // case A -- fix the group ID
            // 
            // This is safe because /Library is sticky and the file is owned 
            // by root, which means that only root can move it.  Also, we 
            // don't have to worry about malicious files existing within the 
            // directory because its only writeable by root.
 
            err = chown(kBASToolDirPath, -1, 0);
            if (err < 0) {
                err = errno;
            }
            fprintf(stderr, "chown -1:0 '%s' -> %d\n", kBASToolDirPath, err);
        } else {
            fprintf(stderr, "bogus perms on '%s' %d:%d %o\n", kBASToolDirPath, (int) sb.st_uid, (int) sb.st_gid, (int) sb.st_mode);
            err = EPERM;
        }
    }
 
    // Then create the known good copy.  The ownership and permissions 
    // will be set appropriately, as described in the comments for mkdir. 
    // We don't have to worry about atomicity because this tool won't be 
    // looked at until our plist is installed.
 
    if (err == 0) {
        err = CopyFileOverwriting(toolSourcePath, kExecutableMode, toolDestPath);
    }
 
    // For the plist, our caller has created the file in /tmp and we just copy it 
    // into the correct location.  This ensures that the file is complete 
    // and valid before anyone starts looking at it and will also overwrite 
    // any existing file with this new version.
    // 
    // Since we have to read/write in the file byte by byte to make sure that 
    // the file is complete we are rolling our own 'copy'. This clearly is 
    // ignoring atomicity since we do not roll back to the state of 'what was 
    // previously there' if there is an error; rather, whatever has been 
    // written up to that point of granular failure /is/ the state of the 
    // plist file.
 
    if (err == 0) {
        err = CopyFileOverwriting(plistSourcePath, kFileMode, plistDestPath);
    }
    
    // Use launchctl to load our job.  The plist file starts out disabled, 
    // so we pass "-w" to enable it permanently.
 
    if (err == 0) {
        err = RunLaunchCtl(false, "load", plistDestPath);
    }
    
    return err;
}
 
static int EnableCommand(
    const char                  *bundleID
)
    // Utility function to call through to RunLaunchCtl in order to load a job
    // given by the path contructed from the (const char *) bundleID.
{
    int     err;
    char    plistPath[PATH_MAX];
    
    // Pre-condition.
    assert(bundleID != NULL);
    
    (void) snprintf(plistPath, sizeof(plistPath), kBASPlistPathFormat, bundleID);
    err = RunLaunchCtl(false, "load", plistPath);
 
    return err;
}
 
int main(int argc, char **argv)
{
    int err;
    
    // Print our PID so that the app can avoid creating zombies.
 
    fprintf(stdout, kBASAntiZombiePIDToken1 "%ld" kBASAntiZombiePIDToken2 "\n", (long) getpid());
    fflush(stdout);
 
    // On the client side, AEWP only gives a handle to stdout, so we dup stdout 
    // downto stderr for the rest of this tool.  This ensures that all our output 
    // makes it to the client.
 
    err = dup2(STDOUT_FILENO, STDERR_FILENO);
    if (err < 0) {
        err = errno;
    } else {
        err = 0;
    }
 
    // Set up the standard umask.  The goal here is to be robust in the 
    // face of common environmental changes, not to resist a malicious attack.
    // Also sync the RUID to the 0 because launchctl keys off the RUID (at least 
    // on 10.4.x).
 
    if (err == 0) {
        (void) umask(S_IWGRP | S_IWOTH);
        
        err = setuid(0);
        if (err < 0) {
            fprintf(stderr, "setuid\n");
            err = EINVAL;
        }
    }
    
    if ( (err == 0) && (argc < 2) ) {
        fprintf(stderr, "usage\n");
        err = EINVAL;
    }
 
    // The first argument is the command.  Switch off that and extract the 
    // remaining arguments and pass them to our command routines.
    
    if (err == 0) {
        if ( strcmp(argv[1], kBASInstallToolInstallCommand) == 0 ) {
            if (argc == 5) {
                err = InstallCommand(argv[2], argv[3], argv[4]);
            } else {
                fprintf(stderr, "usage3\n");
                err = EINVAL;
            }
        } else if ( strcmp(argv[1], kBASInstallToolEnableCommand) == 0 ) {
            if (argc == 3) {
                err = EnableCommand(argv[2]);
            } else {
                fprintf(stderr, "usage4\n");
                err = EINVAL;
            }
        } else {
            fprintf(stderr, "usage2\n");
            err = EINVAL;
        }
    }
 
    // Write "oK" to stdout and quit.  The presence of the "oK" on the last 
    // line of output is used by the calling code to detect success.
    
    if (err == 0) {
        fprintf(stderr, kBASInstallToolSuccess "\n");
    } else {
        fprintf(stderr, kBASInstallToolFailure "\n", err);
    }
    
    return (err == 0) ? EXIT_SUCCESS : EXIT_FAILURE;
}