CVE-2022-50737 in Linux
要約
〜によって VulDB • 2026年06月07日
Based on the kernel log snippet provided, here is an analysis of the crash and the likely cause.
### **Summary** This is a **KASAN (Kernel Address Sanitizer)** report indicating a **use-after-free** or **invalid memory access** in the `__x64_sys_mount` system call. The crash occurred while accessing a memory address that belongs to a **freed physical page** (`refcount:0`, `mapcount:0`).
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### **Detailed Analysis**
#### **1. The Crash Location** - **Function:** `__x64_sys_mount+0xca/0x110` - This indicates the crash happened inside the `mount` system call implementation in the kernel. - **RIP:** `0x7f9d374e948a` - This is a user-space address (starts with `0x7f...`), which is unusual for a kernel crash unless: - The kernel was executing code that was mapped into user space (e.g., via `vmalloc` or `kmap` that leaked, or more likely, **the RIP shown is the user-space instruction pointer that triggered the syscall**, and the kernel stack trace shows where it crashed *inside* the kernel). - **Correction:** In KASAN reports, `RIP` often shows the user-space instruction pointer that caused the fault. The actual kernel crash location is in the stack trace above (`__x64_sys_mount`).
#### **2. The Buggy Address** - **Message:** `The buggy address belongs to the physical page:` - **Page Info:** ``` page:000000003e38a3d5 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x37bc flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff) ``` - **`refcount:0`**: The page has no references. It is **freed**. - **`mapcount:0`**: The page is not mapped in any page table. - **`mapping:0`**: The page is not associated with any file or anonymous memory mapping. - **Conclusion:** The kernel is trying to access memory that has already been freed and returned to the buddy allocator. This is a classic **Use-After-Free (UAF)** bug.
#### **3. Context** - **Syscall:** `mount` (syscall number `0xa5` = 165). - **Registers:** - `RDI`: `0000561cdb442af0` (likely the `mountpoint` path) - `RSI`: `0000561cdb43a2e0` (likely the `source` path) - `RDX`: `0000561cdb43a260` (likely the `type` string) - `R10`: `00000000c0ed0000` (likely the `flags` or `data` pointer)
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### **Likely Cause** The `mount` system call is accessing a pointer that was previously allocated (e.g., for a path, a mount option string, or an internal kernel structure) but has already been freed. This could be due to:
1. **Race Condition:** A pointer is freed by one thread/context while another thread/context is still using it in the `mount` syscall. 2. **Double Free:** The same memory is freed twice, and the second access triggers the UAF. 3. **Invalid Pointer:** A user-space pointer passed to `mount` is invalid or points to freed memory (though KASAN usually catches kernel-side UAFs, not user-space faults directly unless it's a kernel bug).
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### **How to Debug Further**
1. **Check Full KASAN Report:** - The snippet is truncated. Look for the **"BUG: KASAN: use-after-free in ..."** line earlier in the log. It will show the exact function and line where the memory was freed. - Look for the **"freed by"** and **"accessed by"** sections in the full KASAN output. This will tell you: - Which function freed the memory. - Which function accessed it (likely `__x64_sys_mount` or a helper like `path_mount` or `vfs_mount`).
2. **Check for Recent Changes:** - If this is a custom kernel or a specific
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