CVE-2026-31718

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger

When a durable file handle survives session disconnect (TCP close without SMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the handle for later reconnection. However, it did not clean up the byte-range locks on fp->lock_list.

Later, when the durable scavenger thread times out and calls __ksmbd_close_fd(NULL, fp), the lock cleanup loop did:

spin_lock(&fp->conn->llist_lock);

This caused a slab use-after-free because fp->conn was NULL and the original connection object had already been freed by ksmbd_tcp_disconnect().

The root cause is asymmetric cleanup: lock entries (smb_lock->clist) were left dangling on the freed conn->lock_list while fp->conn was nulled out.

To fix this issue properly, we need to handle the lifetime of smb_lock->clist across three paths:

• Safely skip clist deletion when list is empty and fp->conn is NULL.
• Remove the lock from the old connections lock_list in session_fd_check()
• Re-add the lock to the new connections lock_list in ksmbd_reopen_durable_fd().

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0000a7780e0e446a28a273572f6ea8f7f582f694
• https://git.kernel.org/stable/c/235e32320a470fcd3998fb3774f2290a0eb302a1
• https://git.kernel.org/stable/c/3d6682726c2d3a46d31dae88b8166786b09b03ad
• https://git.kernel.org/stable/c/b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9
• https://git.kernel.org/stable/c/e33c65f011980b4ad4abfd93585ec2079856368f