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Harden PowerShell execution with safe SearchPathW and os_spawn

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This commit is contained in:
Andrea Mazzoleni 2026-08-16 22:46:12 +02:00
parent c1fa9e23b6
commit 87977f28f4
2 changed files with 69 additions and 25 deletions
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83
cmdline/mingwapp.c
View file

@ -203,7 +203,7 @@ static int base64_encode(const unsigned char* in, size_t in_len, char* out, size
/*
* PowerShell helper
*
* Runs a PowerShell one-liner via _popen() and captures the first line
* Runs a PowerShell one-liner via os_spawn() and captures the first line
* of stdout into `out` as UTF-8.
* `out` may be NULL when output is not needed.
*
@ -214,13 +214,34 @@ static int base64_encode(const unsigned char* in, size_t in_len, char* out, size
*/
static int windows_ps(const char* ps_command, char* out, size_t out_size)
{
char cmd[PS_CMD_MAX];
WCHAR wps_path[PATH_MAX];
char ps_path[PATH_MAX * 3];
WCHAR wcmd[PS_CMD_MAX / 4];
char b64cmd[PS_CMD_MAX];
FILE* fp;
int ret;
DWORD plen;
int stdout_fd = -1;
pid_t pid;
int status;
int wlen;
/*
* Resolve powershell.exe to an absolute path.
* Safe search mode enabled in os_init() via SetSearchPathMode() ensures
* system directories and PATH are searched before the current working directory.
*/
plen = SearchPathW(NULL, L"powershell.exe", NULL, PATH_MAX, wps_path, NULL);
if (plen == 0 || plen >= PATH_MAX) {
windows_errno(GetLastError());
log_error(errno, "Failed to locate powershell.exe for command '%s'.\n", ps_command);
return -1;
}
if (WideCharToMultiByte(CP_UTF8, 0, wps_path, -1, ps_path, sizeof(ps_path), 0, 0) == 0) {
errno = E2BIG;
log_error(errno, "Failed to convert powershell.exe path for command '%s'.\n", ps_command);
return -1;
}
/* convert UTF-8 command to UTF-16LE WCHARs */
wlen = MultiByteToWideChar(CP_UTF8, 0, ps_command, -1, wcmd, PS_CMD_MAX / 4);
if (wlen <= 0) {
@ -236,38 +257,50 @@ static int windows_ps(const char* ps_command, char* out, size_t out_size)
return -1;
}
ret = snprintf(cmd, sizeof(cmd), "powershell.exe -NoProfile -NonInteractive -EncodedCommand \"%s\" 2>nul", b64cmd);
if (ret < 0 || ret >= (int)sizeof(cmd)) {
errno = EINVAL;
return -1;
}
char* argv[] = {
ps_path,
"-NoProfile",
"-NonInteractive",
"-EncodedCommand",
b64cmd,
0
};
fp = _popen(cmd, "r");
if (!fp) {
windows_errno(GetLastError());
log_error(errno, "Failed to run PowerShell command '%s' (from popen).\n", ps_command);
pid = os_spawn(argv, &stdout_fd, 0, 0);
if (pid < 0) {
log_error(errno, "Failed to run PowerShell command '%s' (from os_spawn).\n", ps_command);
return -1;
}
if (out && out_size > 0) {
/* get the first line */
if (!fgets(out, (int)out_size, fp)) {
out[0] = 0;
} else {
/* trim spaces and newlines */
strtrim(out);
size_t pos = 0;
while (pos + 1 < out_size) {
ssize_t ret = read(stdout_fd, out + pos, out_size - 1 - pos);
if (ret <= 0)
break;
pos += ret;
if (memchr(out, '\n', pos))
break;
}
out[pos] = 0;
/* truncate at first newline and trim */
char* eol = strpbrk(out, "\r\n");
if (eol)
*eol = 0;
strtrim(out);
}
ret = _pclose(fp);
if (ret == -1) {
errno = EINVAL;
log_error(errno, "Failed to run PowerShell command '%s' (from pclose).\n", ps_command);
close(stdout_fd);
status = 0;
if (os_wait(pid, &status) < 0) {
log_error(errno, "Failed to wait for PowerShell command '%s' (from os_wait).\n", ps_command);
return -1;
}
if (ret != 0) {
if (status != 0) {
errno = EINVAL;
log_error(errno, "PowerShell command '%s' failed with '%d' (from pclose).\n", ps_command, ret);
log_error(errno, "PowerShell command '%s' failed with '%d'.\n", ps_command, status);
return -1;
}

11
os/mingw.c
View file

@ -33,6 +33,14 @@
#define WIN32_ES_CONTINUOUS 0x80000000L
#endif
/* For SetSearchPathMode */
#ifndef BASE_SEARCH_PATH_ENABLE_SAFE_SEARCHMODE
#define BASE_SEARCH_PATH_ENABLE_SAFE_SEARCHMODE 0x00000001
#endif
#ifndef BASE_SEARCH_PATH_PERMANENT
#define BASE_SEARCH_PATH_PERMANENT 0x00008000
#endif
/* File Index */
#undef FILE_INVALID_FILE_ID
#define FILE_INVALID_FILE_ID ((ULONGLONG)-1LL)
@ -3611,6 +3619,9 @@ void os_init(unsigned opt)
os_exit();
}
/* enable safe search path mode permanently to prevent binary hijacking from CWD */
SetSearchPathMode(BASE_SEARCH_PATH_ENABLE_SAFE_SEARCHMODE | BASE_SEARCH_PATH_PERMANENT);
dll_advapi32 = LoadLibrary("ADVAPI32.DLL");
if (!dll_advapi32) {
os_syslog(OS_LVL_CRITICAL, "error loading the ADVAPI32 module");