util-lua-bytevarlib.c

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/* Copyright (C) 2025 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */
 
#include "suricata-common.h"
#include "detect-byte.h"
#include "util-lua-common.h"
#include "util-lua-bytevarlib.h"
#include "util-lua.h"
#include "detect-lua.h"
#include "detect-lua-extensions.h"
 
#include "lauxlib.h"
 
static const char suricata_bytevar_mt[] = "suricata:bytevar:mt";
 
/* handle = slot id + the signature whose extractor may have written it */
typedef struct LuaBytevarHandle_ {
    uint32_t id;
    const Signature *sig;
} LuaBytevarHandle;
 
static DetectLuaData *GetLuaData(lua_State *luastate)
{
    return LuaStateGetDetectLuaData(luastate);
}
 
static int LuaBytevarMap(lua_State *L)
{
    DetectLuaData *ld = GetLuaData(L);
    if (ld == NULL) {
        return luaL_error(L, "bytevar API not available in this context");
    }
    /* map() appends to the shared DetectLuaData like the flowvar/flowint
     * register() APIs: only allowed while init() runs */
    if (!ld->register_in_init) {
        return luaL_error(L, "bytevar.map() must be called from init()");
    }
    if (!lua_islightuserdata(L, -2)) {
        return luaL_error(L, "bytevar.map: first argument must be the signature passed to init");
    }
    /* only the exact signature pointer the engine passed to init() is
     * valid; the script could forge other lightuserdata values (e.g. from
     * the registry) and map() must fail closed */
    if (lua_touserdata(L, -2) != (void *)ld->signature) {
        return luaL_error(L, "bytevar.map: first argument is not the signature passed to init");
    }
    const Signature *s = lua_touserdata(L, -2);
    const char *name = luaL_checkstring(L, -1);
 
    /* Is this name already mapped? */
    for (uint16_t i = 0; i < ld->bytevars; i++) {
        if (strcmp(ld->bytevar[i].name, name) == 0) {
            lua_pushinteger(L, ld->bytevar[i].id);
            return 1;
        }
    }
 
    if (ld->bytevars >= DETECT_LUA_MAX_BYTEVARS) {
        return luaL_error(L, "too many bytevars mapped");
    }
 
    DetectByteIndexType idx;
    if (!DetectByteRetrieveSMVar(name, s, -1, &idx)) {
        return luaL_error(L, "unknown byte_extract or byte_math variable: %s", name);
    }
 
    ld->bytevar[ld->bytevars].name = SCStrdup(name);
    if (ld->bytevar[ld->bytevars].name == NULL) {
        return luaL_error(L, "failed to allocate memory for bytevar name: %s", name);
    }
    ld->bytevar[ld->bytevars++].id = idx;
 
    return 1;
}
 
static int LuaBytevarGet(lua_State *L)
{
    const char *name = luaL_checkstring(L, 1);
    DetectLuaData *ld = GetLuaData(L);
    if (ld == NULL) {
        return luaL_error(L, "internal error: no lua data");
    }
 
    for (uint16_t i = 0; i < ld->bytevars; i++) {
        if (strcmp(ld->bytevar[i].name, name) == 0) {
            LuaBytevarHandle *handle = SCLuaNewUserData(L, SCLUA_TUD_BYTEVAR, sizeof(*handle));
            if (handle == NULL) {
                return LuaCallbackError(L, "error: failed to allocate user data");
            }
            handle->id = ld->bytevar[i].id;
            handle->sig = ld->signature;
            luaL_getmetatable(L, suricata_bytevar_mt);
            lua_setmetatable(L, -2);
            return 1;
        }
    }
 
    return luaL_error(L, "unknown bytevar: %s", name);
}
 
static int LuaBytevarValue(lua_State *L)
{
    LuaBytevarHandle *handle = SCLuaCheckUserData(L, 1, suricata_bytevar_mt, SCLUA_TUD_BYTEVAR);
    if (handle == NULL) {
        lua_pushnil(L);
        return 1;
    }
    DetectEngineThreadCtx *det_ctx = LuaStateGetDetCtx(L);
    if (det_ctx == NULL) {
        return LuaCallbackError(L, "internal error: no det_ctx");
    }
 
    const int32_t max_id = det_ctx->de_ctx->byte_extract_max_local_id;
    if ((int32_t)handle->id < 0 || (int32_t)handle->id > max_id) {
        return LuaCallbackError(L, "bytevar index out of range");
    }
 
    /* the slot is only valid once an extractor wrote it this detect
     * run; an unwritten slot is stale (previous run) or uninitialized,
     * so report it as unset rather than leaking that value to the script */
    if (det_ctx->byte_values[handle->id].set == 0) {
        lua_pushnil(L);
        return 1;
    }
 
    /* the local id is shared across signatures (the first extractor of
     * every rule is slot 0): only the value this rule's extractor wrote
     * this run is this rule's to read */
    if (det_ctx->byte_values[handle->id].writer != handle->sig) {
        lua_pushnil(L);
        return 1;
    }
 
    lua_pushinteger(L, det_ctx->byte_values[handle->id].value);
    return 1;
}
 
static const luaL_Reg bytevarlib[] = {
    // clang-format off
    { "map", LuaBytevarMap, },
    { "get", LuaBytevarGet, },
    { NULL, NULL, },
    // clang-format on
};
 
static const luaL_Reg bytevarmt[] = {
    // clang-format off
    { "value", LuaBytevarValue, },
    { NULL, NULL, },
    // clang-format on
};
 
int LuaLoadBytevarLib(lua_State *L)
{
    luaL_newmetatable(L, suricata_bytevar_mt);
    lua_pushvalue(L, -1);
    lua_setfield(L, -2, "__index");
    luaL_setfuncs(L, bytevarmt, 0);
 
    luaL_newlib(L, bytevarlib);
    return 1;
}