CVE-2026-31718

Description

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 connection's lock_list in session_fd_check() - Re-add the lock to the new connection's lock_list in ksmbd_reopen_durable_fd().

Predictions

Heuristic predictions, AS-IS, for prioritization only.

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
• https://www.suse.com/security/cve/CVE-2026-31718.html
• https://security-tracker.debian.org/tracker/CVE-2026-31718
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-31718

CWEs

CWE-416