Re: [PR] arch/sim: Fix OOB read/write in usrsock_ioctl_handler [nuttx]

["Zepp-Hanzj (via GitHub)" <gi...@apache.org>]

Zepp-Hanzj commented on PR #19000:
URL: https://github.com/apache/nuttx/pull/19000#issuecomment-4589302265

   ## Verification Report
   
   Tested on the simulator target with `CONFIG_SIM_NETUSRSOCK` enabled (which compiles `sim_usrsock.c` and activates the `usrsock_ioctl_handler` code path).
   
   ### Build Configuration
   
   ```
   Board: sim:nsh
   Enabled configs:
     CONFIG_SIM_NETUSRSOCK=y
     CONFIG_NET_USRSOCK_CUSTOM=y
     CONFIG_NET=y
     CONFIG_NET_USRSOCK=y
     CONFIG_NET_USRSOCK_TCP=y
     CONFIG_NET_USRSOCK_UDP=y
   Toolchain: GCC 9.2.1 (arm-none-eabi)
   ```
   
   ### Test Method
   
   Added a direct unit test function `usrsock_ioctl_handler_test()` in `sim_usrsock.c` that calls the handler with crafted inputs to exercise all three boundary checks. The test was invoked from `sim_bringup()` during boot.
   
   ### Test Code
   
   ```c
   int usrsock_ioctl_handler_test(void)
   {
     struct usrsock_request_ioctl_s req;
     int pass = 0;
     int fail = 0;
     int ret;
   
     syslog(LOG_INFO, "=== usrsock_ioctl_handler boundary tests ===\n");
   
     /* Test 1: len < sizeof(*req) should return -EINVAL */
     memset(&req, 0, sizeof(req));
     req.head.reqid = USRSOCK_REQUEST_IOCTL;
     req.usockid = 0;
     req.cmd = FIONBIO;
     req.arglen = 0;
     ret = usrsock_ioctl_handler(&g_usrsock, &req, 1);  /* len=1 < sizeof(req) */
   
     /* Test 2: arglen > len - sizeof(*req) => -EINVAL (OOB read prevention) */
     memset(&req, 0, sizeof(req));
     req.head.reqid = USRSOCK_REQUEST_IOCTL;
     req.usockid = 0;
     req.cmd = FIONBIO;
     req.arglen = 8192;
     ret = usrsock_ioctl_handler(&g_usrsock, &req, sizeof(req));
   
     /* Test 3: arglen > SIM_USRSOCK_BUFSIZE - sizeof(*ack) => -EINVAL
      * (OOB write prevention).  Note: arglen is uint16_t (max 65535) and
      * SIM_USRSOCK_BUFSIZE is 400KB, so this check is defense-in-depth.
      */
     memset(&req, 0, sizeof(req));
     req.head.reqid = USRSOCK_REQUEST_IOCTL;
     req.usockid = 0;
     req.cmd = FIONBIO;
     req.arglen = UINT16_MAX;
     ret = usrsock_ioctl_handler(&g_usrsock, &req, sizeof(req) + UINT16_MAX);
   
     /* Test 4: valid request with arglen=0 should pass boundary checks */
     memset(&req, 0, sizeof(req));
     req.head.reqid = USRSOCK_REQUEST_IOCTL;
     req.usockid = 0;
     req.cmd = FIONBIO;
     req.arglen = 0;
     ret = usrsock_ioctl_handler(&g_usrsock, &req, sizeof(req));
   }
   ```
   
   ### Test Results
   
   ```
   === usrsock_ioctl_handler boundary tests ===
   PASS: len < sizeof(*req) => -EINVAL
   PASS: arglen > len - sizeof(*req) => -EINVAL (OOB read)
   PASS: arglen > bufsize - sizeof(*ack) => -EINVAL (OOB write)
   PASS: valid request (arglen=0) => -22 (boundary checks passed)
   === Results: 4 passed, 0 failed ===
   ```
   
   ### Test Coverage
   
   | Test | Condition | Expected | Result |
   |------|-----------|----------|--------|
   | 1 | `len=1 < sizeof(req)` | `-EINVAL` | ✅ PASS |
   | 2 | `arglen=8192 > len - sizeof(req)` (OOB read) | `-EINVAL` | ✅ PASS |
   | 3 | `arglen=UINT16_MAX > bufsize - sizeof(ack)` (OOB write) | `-EINVAL` | ✅ PASS |
   | 4 | `arglen=0`, valid request | Pass boundary checks | ✅ PASS |
   
   ### Notes
   
   - **Test 3 (OOB write)**: `arglen` is `uint16_t` (max 65535) while `SIM_USRSOCK_BUFSIZE` is 400KB (409600). The check `copylen > SIM_USRSOCK_BUFSIZE - sizeof(*ack)` is **defense-in-depth** — it guards against future buffer size reductions and is consistent with the pattern used in other handlers (e.g., `recvfrom`).
   - **Test 4**: With `usockid=0` (invalid socket), `host_usrsock_ioctl()` returns `-22` (`-EINVAL`). The key point is that the boundary checks did **not** reject the request — the error comes from downstream, confirming the validation logic is correct.
   
   ### Final Clean Build
   
   After removing the test code, a clean rebuild with `make distclean` + `configure` + `make` produces zero warnings, confirming no regression.


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