CVE-2026-63979net/handshake: hand off the pinned file reference to accept_doit

Official description

In the Linux kernel, the following vulnerability has been resolved: net/handshake: hand off the pinned file reference to accept_doit handshake_req_next() removes the request from the per-net pending list and drops hn_lock before handshake_nl_accept_doit() reads req->hr_sk->sk_socket and dereferences sock->file (once in FD_PREPARE() and again in get_file()). In that window a consumer running tls_handshake_cancel() followed by sockfd_put() (svc_sock_free) or __fput_sync() (xs_reset_transport) releases sock->file. sock_release() then runs sock_orphan(), zeroing sk_socket, and frees the struct socket. The accept-side code either reads NULL through sk_socket or chases freed memory. The submit-side sock_hold() does not prevent this. sk_refcnt protects struct sock, but struct socket and sock->file are independently refcounted via the file descriptor the consumer owns. Pinning sk leaves sock and sock->file unprotected. Retarget the accept-side dereferences at req->hr_file, which was pinned at submit time, instead of req->hr_sk->sk_socket->file. Pinning on its own is not sufficient: a consumer that cancels between handshake_req_next() returning and accept_doit reaching FD_PREPARE() takes the !remove_pending() branch in handshake_req_cancel() and drops hr_file before the accept side takes its own reference. Hand off an additional file reference inside handshake_req_next(), under hn_lock, so the accept side operates on a reference that no concurrent handshake_req_cancel() can revoke. FD_PREPARE() consumes that handed-off reference, either by transferring it to the new fd in fd_publish() or by dropping it in the cleanup destructor on error; the explicit get_file() that previously balanced FD_PREPARE() is therefore redundant and goes away. Update handshake_req_cancel_test2 and _test3 to simulate the FD_PREPARE() consumption with an fput() so the kunit file-count assertions stay balanced.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/b869e3e4ce1996df23b3efdbbe9a64c4ab81d745
• https://git.kernel.org/stable/c/2f28dbb30b88eafab8d49aaec94710b4e12dea8e
• https://git.kernel.org/stable/c/68eba6519cbd6359fb554a9720f3a3b6b2eba23f
• https://git.kernel.org/stable/c/c06876d4fac38f35820946ee3b1be7d7da799cd4
• https://git.kernel.org/stable/c/f4251190e58b209999c1ba9e6d2976136a1be055