Bug 2429063 (CVE-2025-68775)

Summary: CVE-2025-68775 kernel: net/handshake: duplicate handshake cancellations leak socket
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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OS: Linux   
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A race condition flaw was found in the Linux kernel's network handshake subsystem. When duplicate handshake cancellation requests arrive for the same TLS handshake (such as during SUNRPC/NFS TLS negotiation timeouts), the code fails to detect the duplicate and incorrectly manipulates the socket reference count, leading to a refcount underflow and potential socket resource leak.
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Description OSIDB Bzimport 2026-01-13 16:04:03 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net/handshake: duplicate handshake cancellations leak socket

When a handshake request is cancelled it is removed from the
handshake_net->hn_requests list, but it is still present in the
handshake_rhashtbl until it is destroyed.

If a second cancellation request arrives for the same handshake request,
then remove_pending() will return false... and assuming
HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue
processing through the out_true label, where we put another reference on
the sock and a refcount underflow occurs.

This can happen for example if a handshake times out - particularly if
the SUNRPC client sends the AUTH_TLS probe to the server but doesn't
follow it up with the ClientHello due to a problem with tlshd.  When the
timeout is hit on the server, the server will send a FIN, which triggers
a cancellation request via xs_reset_transport().  When the timeout is
hit on the client, another cancellation request happens via
xs_tls_handshake_sync().

Add a test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel
path so duplicate cancels can be detected.
Comment 1 Jon Moroney 2026-01-15 02:03:15 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026011359-CVE-2025-68775-6e68@gregkh/T