CVE-2026-64401

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

smb: client: resolve SWN tcon from live registrations

cifs_swn_notify() looks up a witness registration by id under

cifs_swnreg_idr_mutex, drops the mutex, and then uses the registration's

cached tcon pointer. That pointer is not a lifetime reference, and it is

not a stable representative once cifs_get_swn_reg() lets multiple tcons

for the same net/share name share one registration id.

A same-share second mount can keep the cifs_swn_reg alive after the first

tcon unregisters and is freed. The registration then still points at the

freed first tcon, so taking tc_lock or incrementing tc_count through

swnreg->tcon only moves the use-after-free earlier. Taking tc_lock while

holding cifs_swnreg_idr_mutex also violates the documented CIFS lock

order.

Fix this by making the registration store only the stable witness

identity: id, net name, share name, and notify flags. When a notify

arrives, copy that identity under cifs_swnreg_idr_mutex, drop the mutex,

then find and pin a live witness tcon that currently matches the net/share

pair under the normal cifs_tcp_ses_lock -> tc_lock order. The notification

path uses that pinned tcon directly and drops the reference when done.

Registration and unregister messages now use the live tcon passed by the

caller instead of a cached tcon in the registration. The final unregister

send is folded into cifs_swn_unregister() while the registration is still

protected by cifs_swnreg_idr_mutex. This removes the previous

find/drop/reacquire raw-pointer window. The release path only removes the

idr entry and frees the stable identity strings.

This preserves the intended one-registration/many-tcon behavior: a

registration id represents a net/share pair, and notify handling acts on a

live representative selected at use time. It also preserves CLIENT_MOVE

ordering for the representative tcon because the old-IP unregister is sent

before cifs_swn_register() sends the new-IP register.