CVE-2025-21692 in Linux
Сводка
по VulDB • 07.08.2026
Based on the kernel log snippet provided, here is an analysis of what happened and how to proceed.
### **Summary** This is a **kernel panic/oops** triggered by a user-space application making a system call that resulted in an invalid memory access or illegal instruction inside the kernel. The crash occurred during `x64_sys_call`, specifically while handling syscall number `0x2e` (which corresponds to `getrandom()` on x86_64 Linux).
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### **Key Details from the Log**
1. **RIP: `0033:0x44a957`** * This is the instruction pointer where the crash occurred. * The segment selector `0033` indicates user-space code (DS/ES=0x2b, CS=0x33). However, in kernel oops logs, this often points to **user-space memory** that was being accessed incorrectly by a buggy driver or kernel module, OR it’s the address of the faulting instruction within the application itself if the crash happened during return-to-user mode. * Given `RAX: ffffffffffffffda` (which is `-22`, i.e., `-EINVAL`) and `ORIG_RAX: 0x2e`, this suggests the syscall failed with an error, but something went wrong in handling it or returning from it.
2. **System Call Number: `0x2e`** * On x86_64 Linux, syscall number `0x2e` is **`getrandom()`**. * This function retrieves random bytes for cryptographic purposes. It’s commonly used by applications like SSH daemons, web servers (Node.js, Python), or any app needing secure randomness at startup.
3. **Registers** * `RAX: ffffffffffffffda` → `-22` (`-EINVAL`) – Invalid argument error returned from the syscall. * `ORIG_RAX: 0x000000000000002e` → Confirms it was a `getrandom()` call. * `RDI: 3`, `RSI: ...fb70`, `RDX: 0` – Arguments to the syscall (buffer pointer, length=0? flags).
4. **Call Trace** * The trace shows normal entry into system calls (`do_syscall_64`, `x64_sys_call`). * There are no obvious kernel module names in the visible part of the stack, which suggests either: - A core VFS/security subsystem issue. - A bug in how the kernel handles a specific edge case for `getrandom()`. - Or more likely: **The crash happened during return-to-user mode**, and the RIP points to user-space code that was corrupted or misaligned, causing an invalid instruction fetch when returning from the syscall.
5. **"clear_bhb_loop"** * This is a speculative execution mitigation loop (Branch History Buffer) used on some Intel CPUs (like Alder Lake/Raptor Lake). Its presence in the stack suggests CPU-specific mitigations were active during the fault, but it’s likely not the root cause — just part of the context.
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### **Likely Causes**
1. **Buggy User-Space Application**: - The application calling `getrandom()` may have passed an invalid buffer pointer or corrupted its own stack/registers before making the syscall, leading to a kernel panic during argument validation or return handling. - Example: A race condition in multi-threaded code where memory is freed while being accessed by another thread doing `getrandom()`.
2. **Kernel Bug**: - Rarely, there can be bugs in the `getrandom()` implementation under specific conditions (e.g., with certain seccomp filters, namespaces, or cgroups). However, this would usually show kernel function names higher up in the stack if it crashed *inside* a kernel routine.
3. **Hardware/Driver Issue**: - If you have custom hardware drivers that hook into syscall paths (e.g., via `ptrace`, eBPF, or security modules like SELinux/AppArmor), they might be causing corruption.
4. **Corrupted User-Space Binary**: - The RIP `0x44a957` is a user-space address. If the kernel tried to return control to this instruction but it was invalid (e.g., due to memory corruption, heap overflow in the app), you might see such an oops during syscall exit.
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### **How to Debug Further**
1. **Identify the Crashing Process**: - Check `dmes
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