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Run PowerShell commands safely via base64 encoded strings

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This commit is contained in:
Andrea Mazzoleni 2026-07-06 17:53:25 +02:00
parent 33cdd356a0
commit f078eede75
1 changed files with 49 additions and 8 deletions
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57
cmdline/mingwapp.c
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@ -163,10 +163,39 @@ size_t windows_direct_size(void)
#define WINDOWS_NTFS_MAGIC 0x5346544E /* 'N','T','F','S' */
#define PS_CMD_MAX 4096
#define PS_CMD_MAX 16384
#define SNAPSHOT_GUID ".guid"
static const char b64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static void base64_encode(const unsigned char* in, size_t in_len, char* out, size_t out_max)
{
size_t i, j = 0;
for (i = 0; i < in_len; i += 3) {
uint32_t val = 0;
int count = 0;
int k;
for (k = 0; k < 3; ++k) {
val <<= 8;
if (i + k < in_len) {
val |= in[i + k];
++count;
}
}
if (j + 4 >= out_max)
break;
out[j++] = b64chars[(val >> 18) & 0x3F];
out[j++] = b64chars[(val >> 12) & 0x3F];
out[j++] = (count > 1) ? b64chars[(val >> 6) & 0x3F] : '=';
out[j++] = (count > 2) ? b64chars[val & 0x3F] : '=';
}
out[j] = 0;
}
/*
* PowerShell helper
*
@ -174,19 +203,31 @@ size_t windows_direct_size(void)
* of stdout into `out` as UTF-8.
* `out` may be NULL when output is not needed.
*
* The caller builds `command` as a string using snprintf().
* Any embedded path literals must use single quotes so they survive
* the outer double-quote wrapping passed to cmd.exe.
* The command is executed using -EncodedCommand (Base64 UTF-16LE) to safely
* handle any shell metacharacters or quotes in paths and volume names.
*
* Returns 0 on success, -1 on failure.
*/
static int windows_ps(const char* ps_command, char* out, size_t out_size)
{
char cmd[PS_CMD_MAX];
WCHAR wcmd[PS_CMD_MAX];
char b64cmd[PS_CMD_MAX];
FILE* fp;
int ret;
int wlen;
ret = snprintf(cmd, sizeof(cmd), "powershell.exe -NoProfile -NonInteractive -Command \"%s\" 2>nul", ps_command);
/* convert UTF-8 command to UTF-16LE WCHARs */
wlen = MultiByteToWideChar(CP_UTF8, 0, ps_command, -1, wcmd, PS_CMD_MAX);
if (wlen <= 0) {
errno = EINVAL;
return -1;
}
/* base64 encode the UTF-16LE command bytes (excluding the null terminator) */
base64_encode((const unsigned char*)wcmd, (wlen - 1) * sizeof(WCHAR), b64cmd, sizeof(b64cmd));
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;
@ -195,7 +236,7 @@ static int windows_ps(const char* ps_command, char* out, size_t out_size)
fp = _popen(cmd, "r");
if (!fp) {
windows_errno(GetLastError());
log_error(errno, "Failed to run PowerShell command '%s' (from popen).\n", cmd);
log_error(errno, "Failed to run PowerShell command '%s' (from popen).\n", ps_command);
return -1;
}
@ -212,12 +253,12 @@ static int windows_ps(const char* ps_command, char* out, size_t out_size)
ret = _pclose(fp);
if (ret == -1) {
errno = EINVAL;
log_error(errno, "Failed to run PowerShell command '%s' (from pclose).\n", cmd);
log_error(errno, "Failed to run PowerShell command '%s' (from pclose).\n", ps_command);
return -1;
}
if (ret != 0) {
errno = EINVAL;
log_error(errno, "PowerShell command '%s' failed with '%d' (from pclose).\n", cmd, ret);
log_error(errno, "PowerShell command '%s' failed with '%d' (from pclose).\n", ps_command, ret);
return -1;
}