CVE-2026-63978

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

net/handshake: Drain pending requests at net namespace exit

The arguments to list_splice_init() in handshake_net_exit() are

reversed. The call moves the local empty "requests" list onto

hn->hn_requests, leaving the local list empty, so the subsequent

drain loop runs zero iterations. Pending handshake requests that

had not yet been accepted are not torn down when the net namespace

is destroyed; each one keeps a reference on a socket file and on

the handshake_req allocation.

Pass the source and destination in the documented order

(list_splice_init(list, head) moves list onto head) so the pending

list is transferred to the local scratch list and drained through

handshake_complete().

Fixing the splice direction exposes a list-corruption race. After

the splice each req->hr_list still has non-empty link pointers,

threading the stack-local scratch list rather than hn_requests.

A concurrent handshake_req_cancel() -- for example, from sunrpc's

TLS timeout on a kernel socket whose netns reference was not

taken -- finds the request through the rhashtable, calls

remove_pending(), and sees !list_empty(&req->hr_list).

__remove_pending_locked() then list_del_init()s an entry off the

scratch list while the drain iterates, corrupting it. The same

call arriving after the drain loop has run list_del() on an

entry hits LIST_POISON instead.

Have remove_pending() check HANDSHAKE_F_NET_DRAINING under

hn_lock and report not-found when drain is in progress. The

drain has already taken ownership; handshake_complete()'s existing

test_and_set on HANDSHAKE_F_REQ_COMPLETED still arbitrates

between drain and cancel for who calls the consumer's hp_done. Use

list_del_init() rather than list_del() in the drain so req->hr_list

does not carry LIST_POISON after drain releases the entry.

The DRAINING guard in remove_pending() makes cancel return false,

but cancel still falls through to test_and_set_bit on

HANDSHAKE_F_REQ_COMPLETED and drops the request's hr_file reference.

Without another pin, if that is the last reference, sk_destruct frees

the request while it is still linked on the drain loop's local list.

Pin each request's hr_file under hn_lock before releasing the list,

and drop that drain pin after the loop finishes with the request.