ksmbd: don't hold ci->m_lock while waiting for a lease break ack

Overview

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

ksmbd: don't hold ci->m_lock while waiting for a lease break ack

When a cifs.ko client caches a read-handle (RH) lease via deferred close and a conflicting open arrives, ksmbd breaks the lease and waits for the acknowledgment in wait_for_break_ack() for up to OPLOCK_WAIT_TIME (35s). __smb_break_all_levII_oplock() runs that wait while holding ci->m_lock for read.

cifs.ko reacts to a handle-lease break by closing the deferred handle rather than sending a lease break acknowledgment. That close path (close_id_del_oplock() -> opinfo_del()) takes ci->m_lock for write and is exactly what would wake the waiter, but it blocks on the read lock held by the waiting thread. The break is then resolved only by the 35s timeout, so xfstests generic/001 takes ~78s with leases enabled versus ~4s with oplocks only.

Collect the target opinfos (each pinned with a reference) while holding ci->m_lock, then break them after releasing it, matching how smb_grant_oplock() already breaks a conflicting lease using only a reference. The reference keeps the opinfo (and its conn and lease) alive across the unlocked window, and a close racing the break is handled by the existing OPLOCK_CLOSING state check. Apply the same fix to the parent lease break paths.

Affected

• Linux >= d1c189c6cb8b0fb7b5ee549237d27889c40c2f8b < 868c9038ffd4af39766d087f68c8f543a3f66635
• Linux >= d1c189c6cb8b0fb7b5ee549237d27889c40c2f8b < 27a9bc968d4ae809a3f5ca2f2b136856ee613cb4
• Linux 16ece7c5645a68efca22a0a69a7718c8e50c3232
• Linux >= 6.6.35 < 6.7
• Linux 6.9

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.