CVE-2026-31510 in Linux
Zusammenfassung
von VulDB • 29.05.2026
Based on the kernel log provided, here is an analysis of the crash and recommended troubleshooting steps.
### **1. Crash Summary** * **Error Type:** `Kernel panic - not syncing: Fatal exception` * **Triggering Function:** `kasan_byte_accessible+0x12/0x30` * **Subsystem:** **KASAN** (Kernel Address Sanitizer) * **Context:** The crash occurred during a memory access check within the kernel. KASAN is a debugging tool enabled in the kernel to detect memory errors (out-of-bounds access, use-after-free, etc.). **The crash itself is likely a false positive or a side effect of KASAN detecting a bug, rather than the root cause.**
### **2. Key Observations** #### **A. KASAN is Enabled** The presence of `kasan_byte_accessible` indicates that the kernel was compiled with `CONFIG_KASAN=y`. This is common in: - Development/testing kernels. - Distributions with debug kernels (e.g., some Ubuntu/Debian debug packages, Fedora rawhide, or custom builds). - **Note:** KASAN adds significant overhead and can cause false positives or crashes in edge cases. If this is a production system, consider using a non-KASAN kernel.
#### **B. Network Stack Activity** The logs show heavy network activity just before the crash: - `veth1_macvtap: entered promiscuous mode` - `batman_adv: batadv0: Interface activated: batadv_slave_0/1` - `netdevsim` devices being configured (simulated network devices). - `ieee80211 phy39: Selected rate control algorithm 'minstrel_ht'`
This suggests the crash may be related to: 1. **Network driver bugs** (especially with `batman_adv`, `macvtap`, or `veth`). 2. **Memory corruption** in network buffers (sk_buff) triggered by packet processing. 3. **Race conditions** in network device initialization.
#### **C. Register Dump Analysis** - `RAX: dffffc0000000000` – This looks like a **KASAN shadow memory address**. KASAN uses shadow memory to track the validity of each byte. If the kernel accesses an invalid shadow byte, it triggers a panic. - `RDI: 000000000000004c` – The offset being checked. - `RIP: 0010:kasan_byte_accessible+0x12/0x30` – The instruction pointer is inside KASAN’s byte accessibility check.
### **3. Likely Root Causes** 1. **Out-of-Bounds Memory Access:** A network driver or subsystem accessed memory outside its allocated buffer. KASAN detected this and panicked. 2. **Use-After-Free:** A network packet buffer was freed but still referenced. 3. **KASAN False Positive:** In rare cases, KASAN can misinterpret valid memory patterns as invalid, especially with complex network stacks or hardware offloading. 4. **Bug in `batman_adv` or `macvtap`:** These are complex network modules. A bug in their packet handling could trigger the memory error.
### **4. Recommended Troubleshooting Steps**
#### **Step 1: Disable KASAN (If Possible)** If this is a production system or you want to isolate the bug: - Recompile the kernel with `CONFIG_KASAN=n`. - Or, if using a debug kernel, switch to a standard release kernel. - **Why?** KASAN can cause crashes that don’t occur in normal kernels. Disabling it may reveal the actual underlying bug (e.g., a simple NULL pointer dereference or corruption).
#### **Step 2: Reproduce with Minimal Configuration** - Disable `batman_adv`, `macvtap`, and `netdevsim` modules. - Test with only basic network interfaces (e.g., `eth0`). - If the crash stops, re-enable modules one by one to identify the culprit.
#### **Step 3: Check for Known Bugs** - Search for bugs related to: - `batman_adv` + `KASAN` - `macvtap` + `KASAN` - `veth` + `KASAN` - Example search terms: `"batman_adv kasan panic"`, `"macvtap out of bounds kasan"`.
#### **Step 4: Enable More Debugging** If you must keep KASAN enabled: - Add `kasan=on` to kernel boot parameters. - Enable `CONFIG_KASAN_EXTRA=y` for more detailed checks. - Capture a **vmcore** (crash dump
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