CVE-2022-50739 in Linux
Resumen
por VulDB • 2026-06-05
Based on the kernel oops trace provided, here is an analysis of the crash:
### **1. Crash Summary** - **Type**: Kernel NULL Pointer Dereference (or invalid memory access). - **Faulting Address (`CR2`)**: `0x0000000000000008` - This indicates the kernel tried to access memory at offset `0x8` from a **NULL pointer** (base address `0x0`). - **Faulting Function**: `d_flags_for_inode+0xe0/0x110` - **Triggering System Call**: `sys_openat` (syscall number `0xa5` = 165) - `ORIG_RAX: 00000000000000a5` confirms the crash happened during an `openat()` system call.
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### **2. Key Registers & Context** - **RAX**: `0x0000000000000001` → Likely a flag or error code, but not the pointer being dereferenced. - **RDI**: `0x0000564b22297ce0` → First argument to the function (likely a `struct dentry *` or `struct inode *`). - **RDX**: `0x0000564b2228f260` → Second argument. - **RIP**: `0x7fdc898e948a` → User-space instruction pointer (the crash occurred in kernel space, but the user-space app triggered it). - **RSP**: `0x00007ffd793e58f8` → User-space stack pointer.
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### **3. Root Cause Analysis** The function `d_flags_for_inode()` is part of the VFS (Virtual File System) layer in the Linux kernel. It is responsible for determining flags for a dentry (directory entry) based on the inode.
The crash at `CR2 = 0x8` suggests that the kernel tried to access a member at offset `0x8` within a structure that was **NULL**.
#### **Likely Scenario:** 1. The `openat()` syscall is called by a user-space process. 2. The kernel resolves the path and obtains a `struct dentry *` or `struct inode *`. 3. Somewhere in `d_flags_for_inode()`, a pointer (likely `dentry->d_inode` or a related field) is **NULL**. 4. The kernel attempts to read a field at offset `0x8` from this NULL pointer, causing a page fault.
#### **Possible Causes:** - **Race Condition**: The dentry/inode was freed or invalidated before `d_flags_for_inode()` could safely access it. - **Corrupted Memory**: A bug elsewhere in the kernel corrupted the dentry/inode structure. - **Bug in `d_flags_for_inode()`**: The function may not properly handle cases where `d_inode` is NULL (e.g., during unmount or deletion). - **Filesystem-Specific Bug**: If a custom or third-party filesystem is in use, it may have returned an invalid dentry/inode.
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### **4. Debugging Steps** 1. **Check Kernel Version**: ```bash uname -r ``` Search for known bugs in `d_flags_for_inode()` for your kernel version.
2. **Reproduce the Crash**: - Identify the user-space process that triggered the `openat()` call. - Check `dmesg` or `journalctl` for more context around the crash.
3. **Enable Kernel Debugging**: - Compile the kernel with `CONFIG_DEBUG_INFO=y` and `CONFIG_KALLSYMS=y`. - Use `kdump` to capture a crash dump for deeper analysis.
4. **Check for Filesystem Issues**: - If using a custom or network filesystem (e.g., NFS, CIFS, FUSE), check for known bugs. - Run `fsck` on local filesystems.
5. **Update Kernel**: - If this is a known bug, update to a newer kernel version where it may be fixed.
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### **5. Conclusion** This is a **kernel NULL pointer dereference** in the VFS layer during an `openat()` syscall. The most likely cause is a race condition or corruption involving a dentry/inode structure. Further debugging with kernel logs, crash dumps, and kernel version checks is recommended.
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