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/* vi: set sw=4 ts=4: */
/*
* drop - run a command without elevated privileges.
*
* Copyright (c) 2023 Ronald M Yorston
*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
//config:config DROP
//config: bool "drop"
//config: default y
//config: depends on PLATFORM_MINGW32 && SH_IS_ASH
//config: help
//config: Run a command without elevated privileges
//config:config CDROP
//config: bool "cdrop"
//config: default y
//config: depends on PLATFORM_MINGW32
//config: help
//config: Run a command without elevated privileges using cmd.exe
//config:config PDROP
//config: bool "pdrop"
//config: default y
//config: depends on PLATFORM_MINGW32
//config: help
//config: Run a command without elevated privileges using PowerShell
//applet:IF_DROP(APPLET(drop, BB_DIR_USR_BIN, BB_SUID_DROP))
//applet:IF_CDROP(APPLET_ODDNAME(cdrop, drop, BB_DIR_USR_BIN, BB_SUID_DROP, cdrop))
//applet:IF_PDROP(APPLET_ODDNAME(pdrop, drop, BB_DIR_USR_BIN, BB_SUID_DROP, pdrop))
//kbuild:lib-$(CONFIG_DROP) += drop.o
//kbuild:lib-$(CONFIG_CDROP) += drop.o
//kbuild:lib-$(CONFIG_PDROP) += drop.o
//usage:#define drop_trivial_usage
//usage: "[COMMAND | -c [ARG...]]"
//usage:#define drop_full_usage "\n\n"
//usage: "Drop elevated privileges and run a command. If no COMMAND\n"
//usage: "is provided run the BusyBox shell.\n"
//usage:#define cdrop_trivial_usage
//usage: "[COMMAND | /c [ARG...]]"
//usage:#define cdrop_full_usage "\n\n"
//usage: "Drop elevated privileges and run a command. If no COMMAND\n"
//usage: "is provided run cmd.exe.\n"
//usage:#define pdrop_trivial_usage
//usage: "[COMMAND | -c [ARG...]]"
//usage:#define pdrop_full_usage "\n\n"
//usage: "Drop elevated privileges and run a command. If no COMMAND\n"
//usage: "is provided run PowerShell.\n"
#include "libbb.h"
#include <winsafer.h>
#include <lazyload.h>
#include "NUM_APPLETS.h"
// Set an environment variable to the name of the unprivileged user,
// but only if it was previously unset or contained "root".
static void setenv_name(const char *key)
{
const char *name = get_user_name();
const char *oldname = getenv(key);
if (name && (!oldname || strcmp(oldname, "root") == 0)) {
setenv(key, name, 1);
}
}
int drop_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int drop_main(int argc, char **argv)
{
SAFER_LEVEL_HANDLE safer;
HANDLE token;
STARTUPINFO si;
PROCESS_INFORMATION pi;
TOKEN_MANDATORY_LABEL TIL;
// Medium integrity level S-1-16-8192
unsigned char medium[12] = {
0x01, 0x01, 0x00, 0x00,
0x00, 0x00, 0x00, 0x10,
0x00, 0x20, 0x00, 0x00
};
DWORD code;
// This shouldn't be necessary but without it the binary complains
// it can't find CreateProcessAsUserA on older versions of Windows.
DECLARE_PROC_ADDR(BOOL, CreateProcessAsUserA, HANDLE, LPCSTR, LPSTR,
LPSECURITY_ATTRIBUTES, LPSECURITY_ATTRIBUTES, BOOL, DWORD,
LPVOID, LPCSTR, LPSTARTUPINFOA, LPPROCESS_INFORMATION);
if (!INIT_PROC_ADDR(advapi32.dll, CreateProcessAsUserA))
bb_simple_error_msg_and_die("not supported");
/*
* Run a shell using a token with reduced privilege. Hints from:
*
* https://stackoverflow.com/questions/17765568/
*/
if (SaferCreateLevel(SAFER_SCOPEID_USER, SAFER_LEVELID_NORMALUSER,
SAFER_LEVEL_OPEN, &safer, NULL) &&
SaferComputeTokenFromLevel(safer, NULL, &token, 0, NULL)) {
// Set medium integrity
TIL.Label.Sid = (PSID)medium;
TIL.Label.Attributes = SE_GROUP_INTEGRITY;
if (SetTokenInformation(token, TokenIntegrityLevel, &TIL,
sizeof(TOKEN_MANDATORY_LABEL))) {
char **a = argv + 1;
const char *arg;
char *exe, *cmd;
if (argc == 1 || strcmp(argv[1], "-c") == 0
IF_CDROP(|| strcmp(argv[1], "/c") == 0)) {
switch (*applet_name) {
#if ENABLE_PDROP
case 'p':
arg = "powershell.exe";
exe = find_first_executable(arg);
break;
#endif
#if ENABLE_CDROP
case 'c':
arg = "cmd.exe";
exe = find_first_executable(arg);
break;
#endif
#if ENABLE_DROP
case 'd':
arg = "sh";
exe = xstrdup(bb_busybox_exec_path);
break;
#endif
default:
// Never executed, just to silence warnings.
arg = argv[0];
exe = NULL;
break;
}
} else {
arg = *a++;
#if ENABLE_FEATURE_PREFER_APPLETS && NUM_APPLETS > 1
if (!has_path(arg) && find_applet_by_name(arg) >= 0) {
exe = xstrdup(bb_busybox_exec_path);
} else
#endif
if (has_path(arg)) {
exe = file_is_win32_exe(arg);
} else {
exe = find_first_executable(arg);
}
}
if (exe == NULL) {
xfunc_error_retval = 127;
bb_error_msg_and_die("can't find '%s'", arg);
}
slash_to_bs(exe);
cmd = quote_arg(arg);
// Build the command line
while (*a) {
char *q = quote_arg(*a++);
cmd = xappendword(cmd, q);
free(q);
}
ZeroMemory(&si, sizeof(STARTUPINFO));
si.cb = sizeof(STARTUPINFO);
si.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
si.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
si.hStdError = GetStdHandle(STD_ERROR_HANDLE);
si.dwFlags = STARTF_USESTDHANDLES;
setenv_name("USER");
setenv_name("USERNAME");
setenv_name("LOGNAME");
if (!CreateProcessAsUserA(token, exe, cmd, NULL, NULL, TRUE,
0, NULL, NULL, &si, &pi)) {
xfunc_error_retval = 126;
bb_error_msg_and_die("can't execute '%s'", exe);
}
WaitForSingleObject(pi.hProcess, INFINITE);
if (GetExitCodeProcess(pi.hProcess, &code)) {
return (int)code;
}
}
}
return EXIT_FAILURE;
}
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