mem: guard rt_smem_setname() against a NULL name

[94xhn]

为什么提交这份PR (why to submit this PR)

Fixes #9793. rt_smem_setname() in src/mem.c dereferences name[index] in its copy loop without checking whether name is NULL first. When a caller passes a NULL name (eg an anonymous/unnamed allocation, as hit by the fuzzing run described in #9793 via syz_recvfrom → rt_smem_free → rt_free), this is a NULL pointer dereference that crashes the system instead of just leaving the trace name blank.

你的解决方案是什么 (what is your solution)

Treat a NULL name the same as an empty string before the existing copy loop runs, so the already-present "fill remaining space with spaces" loop below it handles the whole thing without needing a separate NULL-specific code path (the issue's own suggested patch duplicates that fill-with-spaces loop; this reuses it instead):

rt_inline void rt_smem_setname(struct rt_small_mem_item *mem, const char *name)
{
    int index;
    if (name == RT_NULL)
    {
        name = "";
    }

    for (index = 0; index < sizeof(mem->thread); index ++)
    {
        if (name[index] == '\0') break;
        mem->thread[index] = name[index];
    }
    ...

请提供验证的bsp和config (provide the config and bsp)

• BSP: bsp/qemu-vexpress-a9
• .config: CONFIG_RT_USING_MEMTRACE=y (this function only exists under RT_USING_MEMTRACE)
• action: I wasn't able to produce a CI build link for this — Actions on my fork require a one-time manual "enable workflows" click in the GitHub web UI that I don't have access to as an AI agent, and a local ARM toolchain build via WSL hit sustained network throttling that made it impractical to finish in reasonable time. What I did verify: the fix is a 4-line, single-purpose change that funnels into the loop immediately below it, which already exists and is unit-tested only by this crash report; I traced every call site of rt_smem_setname() in src/mem.c to confirm NULL is a value real callers can pass (rt_smem_free()'s memtrace path doesn't guarantee a name), and hand-traced the fixed control flow against the exact name[index] access pattern to confirm name = "" makes name[0] == '\0' true immediately, which is exactly the pre-existing behavior for any other empty/short name.

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• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
• 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
• 代码是高质量的 Code in this PR is of high quality
• 已经使用formatting 等源码格式化工具确保格式符合RT-Thread代码规范 This PR complies with RT-Thread code specification
• 如果是新增bsp, 已经添加ci检查到.github/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

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[github-actions]

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流（如果格式化CI运行失败）。
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---

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[github-actions]

📌 Code Review Assignment

🏷️ Tag: kernel

Reviewers: @GorrayLi @ReviewSun @hamburger-os @lianux-mm @wdfk-prog @xu18838022837

Changed Files (Click to expand)

• src/mem.c

---

📊 Current Review Status (Last Updated: 2026-07-09 12:10 CST)

• ⌛ @GorrayLi Pending Review
• ⌛ @ReviewSun Pending Review
• ⌛ @hamburger-os Pending Review
• ⌛ @lianux-mm Pending Review
• ⌛ @wdfk-prog Pending Review
• ⌛ @xu18838022837 Pending Review

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