CVE-2024-56765 in Linux
Riassunto
di VulDB • 01/07/2026
Based on the kernel log provided, this is a **KASAN (Kernel Address Sanitizer)** report indicating a **Use-After-Free** bug in the Linux kernel.
### ???? Summary of the Bug * **Type:** Use-After-Free (UAF) or Double Free detection by KASAN. * **Affected Object:** `vm_area_struct` (VMA), which represents a memory mapping area (e.g., heap, stack, mmap regions). * **Cache Size:** 168 bytes. * **Triggering System Call:** `sys_munmap` → `do_vmi_align_munmap`. This means the bug occurs when an application calls `mun()` to unmap a memory region. * **Root Cause Analysis:** The kernel is trying to free a VMA that has already been freed, or it is accessing a VMA after its RCU grace period has ended but before proper cleanup synchronization occurred.
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### ???? Key Stack Trace Breakdown
#### 1. Where the bug was detected (Free/Access): ```text __kasan_slab_free+0x120/0x204 # KASAN intercepting a slab free kmem_cache_free # Actual memory free call vm_area_free_rcu_cb # RCU callback for freeing VMA rcu_do_batch # Processing RCU callbacks handle_softirqs # SoftIRQ handler (RCU runs in softirq context) ... ``` > **Interpretation:** The kernel is executing an RCU deferred free (`vm_area_free_rcu_cb`) and KASAN detects that the memory being freed was already invalid or double-freed.
#### 2. Where the object was originally created/last used: ```text __call_rcu_common # Scheduling a callback for later freeing vm_area_free # Initiating VMA free (via RCU) remove_vma # Removing a VMA from the mm_struct do_vmi_align_munmap # Core munmap logic handling aligned unmaps __vm_munmap # Internal mmap/munmap helper sys_munmap # System call entry point for `munmap()` ```
#### 3. The Buggy Address: ```text The buggy address belongs to the object at c00000014a819670 which belongs to the cache vm_area_struct of size 168 The buggy address is located 0 bytes inside of freed 168-byte region [c00000014a819670, c00000014a819718)
``` > **Interpretation:** The entire VMA structure (168 bytes) is being accessed/freed again after it was already freed.
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### ????️ Likely Causes & Fixes
This bug typically arises in one of the following scenarios:
#### ✅ 1. Double Free or Incorrect RCU Usage - **Cause:** A code path frees a VMA via `vm_area_free()` (which schedules an RCU callback), but another part of the kernel still holds a reference to that VMA and tries to free it again, or accesses it after the RCB has run. - **Fix:** Ensure that every `vma` is freed exactly once. Check for: - Missing `get_vma()`/`put_vma()` references around access points. - Incorrect use of `remove_vma()` vs direct slab free.
#### ✅ 2. Race Condition in VMA Removal - **Cause:** During `munmap()`, if multiple threads are modifying the same memory map (`mm_struct`) concurrently without proper locking, a VMA might be removed and freed while another thread is still iterating over it. - **Fix:** Ensure that all accesses to VMAs during `munmap()` are protected by appropriate locks (e.g., `mmap_lock`).
#### ✅ 3. Bug in Specific Kernel Version This type of issue has been seen in older kernels or specific subsystems like: - Memory management (`mm/`) - File mapping code that interacts with VMAs incorrectly during unmap operations.
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### ???? How to Debug Further
1. **Reproduce the Issue:** - Identify which application triggered `munmap()`. Use `strace` or `perf record` to capture system calls before the crash. - Example: `strace -e munmap ./your_app`
2. **Check for Recent Patches:** - Search Linux kernel git logs for fixes related to `vm_area_struct`, `munmap`, and KASAN UAF bugs in your specific kernel version. - Keywords: `"kasan vm_area_struct use
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