sunrpc: wait for in-flight TLS handshake callback when cancel loses race

Overview

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

sunrpc: wait for in-flight TLS handshake callback when cancel loses race

When wait_for_completion_interruptible_timeout() in svc_tcp_handshake() returns 0 (timeout) or -ERESTARTSYS (signal) and tls_handshake_cancel() then returns false, handshake_complete() has won the cancellation race: it has set HANDSHAKE_F_REQ_COMPLETED and is about to invoke svc_tcp_handshake_done(), but the callback's side effects on xpt_flags and on svsk->sk_handshake_done have not yet committed.

The current code reads xpt_flags immediately to decide whether the session succeeded. Two races result.

If the callback has executed set_bit(XPT_TLS_SESSION) but not yet clear_bit(XPT_HANDSHAKE), svc_tcp_handshake() sees a session, enqueues the transport, and returns. svc_xprt_received() then clears XPT_BUSY, a worker thread picks the transport up, the dispatcher in svc_handle_xprt() observes XPT_HANDSHAKE still set, and xpo_handshake is invoked a second time. That svc_tcp_handshake() calls init_completion(&svsk->sk_handshake_done) while the original callback concurrently calls complete_all() on it, corrupting the embedded swait_queue.

If the callback has set HANDSHAKE_F_REQ_COMPLETED but not yet entered svc_tcp_handshake_done(), svc_tcp_handshake() reads XPT_TLS_SESSION as clear and tears the connection down even though the handshake is about to succeed.

Wait for the callback to commit before inspecting xpt_flags. The completion is guaranteed to fire because handshake_complete() invokes svc_tcp_handshake_done() unconditionally once it has set HANDSHAKE_F_REQ_COMPLETED.

Affected

• Linux >= b3cbf98e2fdf3cb147a95161560cd25987284330 < 0d8ceb39884148dc7a2fdf71e1cac5961ed1d2b9
• Linux >= b3cbf98e2fdf3cb147a95161560cd25987284330 < e0f4691d42a54d359d8b64509fd9ab938d4f2a33
• Linux >= b3cbf98e2fdf3cb147a95161560cd25987284330 < 65b23bec1fca6e9ebdc3e6041ebf8c6ab074141b
• Linux >= b3cbf98e2fdf3cb147a95161560cd25987284330 < a4f878e8ecd729ccf2e50993444e217583adeace
• Linux >= b3cbf98e2fdf3cb147a95161560cd25987284330 < d00e32f84ca1a77cb67a3fbf59f58dada95f5a21
• Linux 6.4

Remediation

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