AZL-93725

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

net/handshake: Take a long-lived file reference at submit

handshakenlacceptdoit() needs the file pointer backing req->hrsk->sksocket to survive the window between handshakereqnext() and the subsequent FDPREPARE() and getfile(). The submit-side sockhold() does not provide that. skrefcnt keeps struct sock alive, but struct socket is owned by sock->file: when the consumer fputs the last file reference, sockrelease() tears the socket down regardless of any sock_hold.

Add an hrfile pointer to struct handshakereq and acquire an explicit reference on sock->file during handshakereqsubmit(). handshakecomplete() and handshakereq_cancel() release the reference on the completion-bit-winning path.

The submit error path must also release the file reference, but after rhashtable insertion a concurrent handshakereqcancel() can discover the request and race the error path. Gate the error-path cleanup -- skdestruct restoration, fput, and request destruction -- with testandsetbit(HANDSHAKEFREQCOMPLETED), the same serialization handshakecomplete() and handshakereqcancel() already use. When cancel has already claimed ownership, the submit error path returns without touching the request; socket teardown handles final destruction.

The accept-side dereferences are not yet retargeted; that change comes in the next patch.