lua/sandbox: allow disabling the bytes limit

Meant for setting up from C, where we may use more bytes than expected.

Bug: #8173.

src/util-lua-sandbox.c

@@ -73,7 +73,7 @@ static void *LuaAlloc(void *ud, void *ptr, size_t osize, size_t nsize)
         /* Resizing existing data. */
         ssize_t diff = nsize - osize;
 
-        if (ctx->alloc_bytes + diff > ctx->alloc_limit) {
+        if (ctx->alloc_limit != 0 && ctx->alloc_bytes + diff > ctx->alloc_limit) {
             /* This request will exceed the allocation limit. Act as
              * though allocation failed. */
             ctx->memory_limit_error = true;
@@ -382,6 +382,33 @@ static void HookFunc(lua_State *L, lua_Debug *ar)
     }
 }
 
+uint64_t SCLuaSbResetBytesLimit(lua_State *L)
+{
+    uint64_t cfg_limit = 0;
+    SCLuaSbState *sb = SCLuaSbGetContext(L);
+    if (sb != NULL) {
+        cfg_limit = sb->alloc_limit;
+        sb->alloc_limit = 0;
+    }
+    return cfg_limit;
+}
+
+void SCLuaSbUpdateBytesLimit(lua_State *L)
+{
+    SCLuaSbState *sb = SCLuaSbGetContext(L);
+    if (sb != NULL) {
+        sb->alloc_limit = sb->alloc_bytes + sb->alloc_limit;
+    }
+}
+
+void SCLuaSbRestoreBytesLimit(lua_State *L, const uint64_t cfg_limit)
+{
+    SCLuaSbState *sb = SCLuaSbGetContext(L);
+    if (sb != NULL) {
+        sb->alloc_limit = cfg_limit;
+    }
+}
+
 /**
  * Reset the instruction counter for the provided state.
  */

src/util-lua-sandbox.h

@@ -88,4 +88,47 @@ void SCLuaSbResetInstructionCounter(lua_State *sb);
  */
 void SCLuaSbLoadLibs(lua_State *L);
 
+/* alloc_limit (max-bytes) handling. To give the script the full budget
+ * during it's execution, temporary disable the limit and then restore
+ * it with the existing use as baseline
+ *
+ * ```
+ *     // get configured limit and reset active limit to 0
+ *     const uint64_t cfg_limit = SCLuaSbResetBytesLimit(tlua->luastate);
+ *     // push some data to the state
+ *     LuaPushStringBuffer(tlua->luastate, input, (size_t)input_len);
+ *     // restore the limit, which may now be lower than `alloc_bytes`.
+ *     SCLuaSbRestoreBytesLimit(tlua->luastate, cfg_limit);
+ *     // update allowance to take `alloc_bytes` as the baseline, so
+ *     // effectively: sb->alloc_bytes + sb->alloc_limit
+ *     SCLuaSbUpdateBytesLimit(tlua->luastate);
+ *
+ *     ... run script, lua_pcall...
+ *
+ *     while (lua_gettop(tlua->luastate) > 0) {
+ *         lua_pop(tlua->luastate, 1);
+ *     }
+ *     // restore the original alloc_limit
+ *     SCLuaSbRestoreBytesLimit(tlua->luastate, cfg_limit);
+ * ```
+ */
+
+/*
+ * Resets the byte limit and returns the existing limit.
+ * Meant to be used to temporarily disable the limit during preparation
+ * time for a script to run. */
+uint64_t SCLuaSbResetBytesLimit(lua_State *L);
+
+/*
+ * Update the alloc_limit to take the pre-script initialization bytes
+ * as the base line.
+ */
+void SCLuaSbUpdateBytesLimit(lua_State *L);
+
+/*
+ * Set the bytes limit. Meant to be used with the value returned from
+ * `SCLuaSbResetBytesLimit`
+ */
+void SCLuaSbRestoreBytesLimit(lua_State *L, const uint64_t cfg_limit);
+
 #endif /*  SURICATA_UTIL_LUA_SANDBOX_H */