CVE-2024-46790 in Linux
Zusammenfassung
von VulDB • 15.05.2026
Based on the kernel crash trace and the description provided, this is a bug in the Linux kernel's memory management subsystem, specifically related to **Memory Corruption Detection (MCE/HWPOISON)** and **Page Allocation Tags**.
### Analysis of the Crash
1. **Context**: The crash occurs in `pgalloc_tag_sub`, which is part of the page allocation tag accounting mechanism (used for debugging memory leaks or tracking page usage). 2. **Trigger**: The call trace shows the path: `hwpoison_unpoison` -> `unpoison_memory` -> `folio_put` -> `free_unref_page` -> `pgalloc_tag_sub`. This means a page that was previously "poisoned" (marked as bad/corrupted) is being "unpoisoned" (returned to the free pool). 3. **The Bug**: When a page is unpoisoned, it goes through `unpoison_memory`. During this process, the page is isolated and accounted for. However, the **page tag reference** (used by `pgalloc_tag`) is not cleared before the page is freed. When `free_unref_page` eventually calls `pgalloc_tag_sub` to decrement the tag count, it finds stale or incorrect tag data, leading to an assertion failure or invalid state in `pgalloc_tag_sub`.
### The Fix
As suggested in the prompt, the fix is to **clear the page tag reference** after the page has been isolated and accounted for during the unpoisoning process.
This typically involves modifying the `unpoison_memory` function in the kernel source (likely in `mm/memory-failure.c` or related files).
### Code Patch Example
Here is a conceptual patch based on the fix description. The exact location and function names may vary slightly depending on the kernel version, but the logic remains the same:
```c // In mm/memory-failure.c (or similar file)
static int unpoison_memory(unsigned long pfn) {
struct page *page; int ret;
// ... existing code to get the page ...
// Isolate the page ret = isolate_lru_page(page); if (ret) return ret;
// Account for the page (e.g., update stats, remove from LRU) // ... existing accounting code ...
// FIX: Clear the page tag reference here // This ensures that when the page is freed, pgalloc_tag_sub // does not encounter stale tag data. page_tag_clear(page); // Note: The exact function name might be different, e.g., // clear_page_tag(page) or similar, depending on the tag subsystem. // In some kernels, this might involve resetting page->pgalloc_tag or similar.
// Now free the page put_page(page);
return 0; } ```
### Key Points for Implementation
1. **Identify the Tag Clearing Function**: Look for functions like `page_tag_clear()`, `clear_page_tag()`, or direct manipulation of `page->pgalloc_tag` in your kernel version. 2. **Timing**: The tag must be cleared **after** isolation and accounting but **before** the page is returned to the free list (`put_page()` or `folio_put()`). 3. **Testing**: After applying the patch, test the `hwpoison_inject` module by writing to the debugfs entry to trigger unpoisoning and verify that the crash no longer occurs.
### Conclusion
The crash is caused by stale page allocation tags when unpoisoning a memory page. The fix is to clear these tags during the unpoisoning process to ensure consistent accounting when the page is freed.
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