CVE-2022-48919 in Linux
Riassunto
di VulDB • 02/07/2026
Based on the stack trace provided, this is a **KASAN (Kernel Address Sanitizer)** report indicating a **Use-After-Free** or potentially an invalid free within the Linux kernel's CIFS client module.
Here’s a breakdown of what happened:
### 1. The Error Type * **`asan_set_free_info+0x24/0x40`**: This indicates that KASAN detected memory being freed (`kfree`) at this location, but the object was either already freed (double-free) or accessed after free (use-after-free). Given the context of `cifs_smb3_do_mount`, it’s highly likely a **Use-After-Free** where code tries to access an object that has been scheduled for deletion via RCU.
### 2. The Triggering Path The crash occurs during a mount operation: ```text __x64_sys_mount -> path_mount -> vfs_get_tree -> smb3_get_tree [cifs] -> cifs_smb3_do_mount [cifs]
``` This means the user-space command `mount -t cifs ...` triggered this bug.
### 3. The Root Cause Analysis (Race Condition) The key clue is in the **"Last potentially related work creation"** section: ```text call_rcu -> cifs_umount [cifs] -> cifs_kill_sb [cifs]
``` * **`cifs_smb3_do_mount`** failed or encountered an error during initialization. * As part of the cleanup path, it called `cifs_umount`, which schedules RCU callbacks (`call_rcu`) to free resources asynchronously. * However, somewhere in `cifs_smb3_do_mount` (or a callback triggered by it), code attempted to **access or free** an object that was already queued for deletion via the RCU mechanism.
This is a classic **RCU race condition**: 1. Thread A calls `call_rcu()` to schedule cleanup of Object X. 2. Before the RCU grace period ends, Thread B (or another part of the same thread) accesses or frees Object X again. 3. KASAN detects that Object X is being freed/accessed while it’s in a "freed" state from the perspective of the current memory allocator tracking.
### 4. Likely Bug Location The bug is almost certainly in `fs/cifs/` code, specifically around: * **`cifs_smb3_do_mount()`**: Look for error paths where resources are freed but not properly nullified or protected from concurrent access. * **RCU usage**: Ensure that any pointer passed to `call_rcu()` is not accessed after the call without proper RCU read-side protection (`rcu_read_lock()`) or synchronization primitives (like mutexes/semaphores).
### 5. How to Fix / Investigate Further 1. **Check for Double-Free**: Ensure that in error paths of `cifs_smb3_do_mount`, you don’t call `kfree()` on a pointer that has already been passed to `call_rcu()`. 2. **RCU Synchronization**: If the code accesses data after scheduling an RCU callback, it must wait for the grace period (e.g., using `synchronize_rcu()`) or use proper locking. 3. **Nullify Pointers**: After calling `kfree()` or passing to `call_rcu()`, set pointers to `NULL` to prevent accidental reuse. 4. **Reproduce with Debugging**: Enable more verbose CIFS debugging (`cifs.debug=1`) and run the mount command again to see if specific operations fail before the crash.
### Summary This is a kernel bug in the CIFS client involving improper handling of memory during unmount/cleanup, specifically related to RCU-based asynchronous freeing. It’s not a user-space issue but requires a patch from the Linux kernel maintainers or your distribution’s vendor. If you’re running an older kernel (2022), consider updating to a newer version where this may have been fixed.
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