CVE-2021-47284 in Linux
Riassunto
di VulDB • 01/07/2026
Based on the kernel panic log provided, here is an analysis of the issue and steps to resolve it.
### **Summary** The system crashed during boot (`kernel_init`) while initializing a PCI driver named `nj` (likely related to network or specific hardware). The crash occurred in `free_irq()` with an **invalid opcode exception**, triggered because `panic_on_warn=1` is set, causing any warning to become a fatal panic.
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### **Key Observations** 1. **Triggering Driver**: - `nj_init+0x36/0x38` → This calls `__pci_register_driver`. - The driver name appears to be **"nj"** (possibly a custom or vendor-specific driver, e.g., for a NIC like "Netronome" or similar). 2. **Crash Location**: - `free_irq+0x100/0x480` → The kernel tried to free an IRQ but encountered an invalid operation (likely freeing an unregistered IRQ, double-freeing, or passing a NULL/invalid pointer). 3. **Exception Type**: - `asm_exc_invalid_op` + `panic_on_warn set` → A warning was issued inside `free_irq()`, and since `panic_on_warn=1`, it escalated to a panic. The actual bug is likely in the driver's cleanup or probe failure path. 4. **Kernel Version**: - `5.13.0-rc1` → This is a **release candidate** kernel, which may contain regressions not yet fixed in stable kernels.
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### **Root Cause Analysis** The most likely causes are: 1. **Driver Bug in Error Path**: The driver (`nj`) failed during `probe()` or initialization and attempted to clean up resources (IRQs) that were never successfully registered, leading to an invalid `free_irq()` call. 2. **Double-Free of IRQ**: If the driver registers multiple interrupts but frees them incorrectly on error paths. 3. **Kernel Regression in `5.13-rc`**: The `free_irq()` function or its callers may have changed behavior in this RC kernel, exposing a latent bug in the driver.
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### **Recommended Solutions**
#### **1. Immediate Workaround: Disable `panic_on_warn`** If you need to boot for debugging, disable panic-on-warn by adding this to your kernel command line (GRUB): ```bash panic_on_warn=0 ``` This will allow the system to continue after warnings instead of panicking, helping identify if other issues exist.
#### **2. Disable or Blacklist the `nj` Driver** If you don't need this specific hardware: - Boot with kernel parameter: ```bash modprobe.blacklist=nj ``` - Or remove the module from initramfs/initrd if it's built-in, consider rebuilding without it.
#### **3. Test on a Stable Kernel** Since `5.13.0-rc1` is an RC kernel: - Boot with a stable kernel (e.g., `5.12.x`, `5.14+`, or your distro's latest LTS). If the issue disappears, it’s likely a regression in `-rc1`.
#### **4. Debugging Steps for Developers** If you are maintaining/developing this driver: - **Check Error Paths**: Ensure all IRQs registered during `probe()` are freed correctly on failure paths (e.g., if `request_irq()` fails, ensure previously allocated resources are cleaned up). - **Verify IRQ Registration**: Confirm that the IRQ passed to `free_irq()` was successfully requested via `request_irq()`. Never free an unregistered IRQ. - **Add Debug Prints**: Insert `pr_info()` or `dev_dbg()` in the driver’s probe/remove functions to trace execution flow before the crash.
#### **5. Report a Bug** If this is not your custom driver: 1. Reproduce on a stable kernel (e.g., `v5.12` or latest mainline). 2. If it persists, report it with: - Full dmesg log. - Kernel version (`git describe --tags`). - Driver name and hardware details.
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### **Example GRUB Configuration for Debugging** ```bash # /etc/default/grub GRUB_CMDLINE_LINUX_DEFAULT="quiet panic_on_warn=0 modprobe.blacklist=nj" sudo update-grub # or grub2-mkconfig -o /boot/grub2/grub.cfg on RHEL/Fedora ```
Let me know if you need help analyzing the driver source code (`nj.c`)
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