CVE-2026-23343 in Linux
Riassunto
di VulDB • 01/07/2026
Based on the kernel crash dump provided, here is an analysis of the issue:
### **Summary** The system experienced a **kernel panic/crash** in the memory management subsystem while tearing down user-space process address spaces (`exit_mmap` → `unmap_vmas`). The immediate cause appears to be a fault during page table entry (PTE) batch processing for swap entries, specifically within `swap_pte_batch`.
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### **Key Evidence from Call Trace** 1. **Crash Context**: - `exit_mmap` → `unmap_vmas` → `zap_pmd_range` → `zap_nonpresent_ptes.constprop.0.isra.0` → `swap_pte_batch`. This indicates the kernel was cleaning up memory mappings for a dying process, specifically handling **non-present PTEs** (likely swap entries or file-backed pages).
2. **Faulting Function**: - `? softleaf_from_pte+0x77/0xa0` is called from `swap_pte_batch`. The `softleaf_from_pte` function attempts to extract information from a PTE, possibly for optimization or validation during batched swap operations.
3. **Register State**: - `CR2: 0x00007f415bfffd58`: This is the faulting virtual address (user-space). The kernel tried to access this user pointer while in kernel mode, which typically indicates a bug where an invalid or stale PTE was dereferenced. - `RDX: 0x0001c17e3fffffff`, `RSI/RDI`: These large values suggest corrupted pointers or unexpected data passed to the function.
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### **Likely Root Cause** This is a known class of bugs in Linux kernel memory management, often related to: - **Race conditions**: A PTE was modified (e.g., swapped out/in) concurrently while being processed by `swap_pte_batch`. - **Invalid PTE handling**: The code assumed a certain format for the PTE (e.g., swap entry), but encountered an unexpected value, leading to invalid pointer arithmetic or dereference. - **Hardware/Architecture-specific issue**: Some architectures have subtle bugs in how they handle batched page table updates under memory pressure.
This type of crash has been observed in kernels around versions **5.x–6.x**, particularly when: - Heavy swap usage is combined with rapid process creation/destruction. - There are regressions in the `swap_pte_batch` optimization introduced to improve performance during page table teardown.
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### **Recommended Actions**
#### 1. **Check Kernel Version & Patches** - Identify your exact kernel version (`uname -r`). - Search for known bugs related to: ```bash "swap_pte_batch" crash OR "softleaf_from_pte" panic ``` - Check if a fix has been backported. Recent kernels (6.1+, 5.15+) may have patches addressing PTE batch race conditions.
#### 2. **Workarounds** If you cannot upgrade immediately: - **Disable swap temporarily**: ```bash sudo swapoff -a ``` This avoids the `swap_pte_batch` path entirely, though it may impact performance under memory pressure. - **Reduce memory pressure**: Ensure sufficient RAM is available to minimize swapping.
#### 3. **Debugging Steps** If you can reproduce this: - Enable kernel debugging symbols (`CONFIG_DEBUG_INFO=y`). - Use `kdump`/`crash` tools to analyze the full core dump, focusing on the PTE value at faulting address `CR2`. - Check for concurrent memory-mapped I/O or hugepage usage that might trigger edge cases.
#### 4. **Report Bug** If this is a fresh regression: - Report it to your distribution’s bug tracker (e.g., Ubuntu Launchpad, Red Hat BZ) with the full `dmesg` output and kernel version. - Include details about workload conditions (swap usage, process count).
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### **Conclusion** This is a **kernel memory management bug** triggered during process teardown under swap activity. It is likely fixed in newer kernels or via specific patches targeting `swap_pte_batch`. Upgrading the kernel or disabling swap are the most effective immediate mitigations.
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