In the Linux kernel, the following vulnerability has been resolved:
sunrpc: pin svc_xprt across the asynchronous TLS handshake callback
svc_tcp_handshake() stores the raw svc_xprt pointer in
tls_handshake_args.ta_data and submits the request through
tls_server_hello_x509(). The handshake core takes only
sock_hold(req->hr_sk); nothing references the embedding struct
svc_sock that svc_tcp_handshake_done() reaches via container_of().
Two close races leave the in-flight callback writing through a freed
svc_sock. svc_sock_free() calls tls_handshake_cancel() and discards
its return value: a false return means handshake_complete() has
already set HANDSHAKE_F_REQ_COMPLETED but hp_done() may not have
finished, yet svc_sock_free() proceeds to kfree(svsk). The
cancel-loser fall-through inside svc_tcp_handshake() itself produces
the same window: when wait_for_completion_interruptible_timeout()
returns <= 0 (timeout or signal) and tls_handshake_cancel() returns
false, the function does not drain, returns, and svc_handle_xprt()
calls svc_xprt_received(), which clears XPT_BUSY and can drop the
last reference. A concurrent close then runs svc_sock_free() while
svc_tcp_handshake_done() is still updating xpt_flags and walking
svsk->sk_handshake_done.
The corruption surfaces as set_bit/clear_bit RMW into the freed
xpt_flags slab slot and as complete_all() walking and writing the
freed wait_queue_head_t list embedded in sk_handshake_done -- a
slab-corruption primitive, not a benign read. The path is reachable
on any TLS-enabled NFS server whenever a connection close overlaps
the tlshd downcall delivery window; the interruptible wait means
signal delivery suffices, not just SVC_HANDSHAKE_TO expiry.
Take svc_xprt_get(xprt) immediately before tls_server_hello_x509()
so the in-flight callback owns its own reference. Release it on the
two edges where the callback is guaranteed not to fire -- submission
failure from tls_server_hello_x509() and a successful
tls_handshake_cancel() -- and at the tail of
svc_tcp_handshake_done() after complete_all().
[cel: rewrote commit message to describe the actual change]
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 9.8
AV:N - The flaw is in nfsd's server-side SUNRPC/TCP TLS handshake (net/sunrpc/svcsock.c), reached when a remote peer connects to port 2049 and sends a pre-authentication AUTH_TLS NULL STARTTLS probe that triggers svc_tcp_handshake() via svcauth_tls_accept().
AC:L - The attacker controls both sides of the race by initiating AUTH_TLS handshakes and concurrently resetting/closing TCP or waiting for SVC_HANDSHAKE_TO while tlshd delivers completion; repeated parallel connections make the overlap window reliably reachable.
PR:N - AUTH_TLS is processed on RPC procedure 0 before credentials are verified, so an unauthenticated remote client can reach svc_tcp_handshake() and the asynchronous callback without any account, export access, or kernel capability.
UI:N - nfsd worker threads automatically accept the TCP connection, process the STARTTLS probe, run the TLS handshake, and handle teardown/completion callbacks without any local user or administrator action.
S:U - Exploitation corrupts kernel memory on the NFS server host itself and does not cross a VM-guest/host, sandbox, or IOMMU security boundary; impact stays within the kernel's security authority.
C:H - svc_tcp_handshake_done() use-after-frees svc_sock and performs set_bit/clear_bit RMW on freed xpt_flags plus complete_all() on freed sk_handshake_done, a slab-corruption UAF that can disclose arbitrary kernel memory.
I:H - The same UAF delivers attacker-timed writes into reclaimed slab slots through atomic bit operations and wait-queue list updates, enabling heap grooming and further kernel memory corruption for arbitrary modification or code execution.
A:H - Slab corruption and UAF during handshake completion can cause kernel oops/panic, and unauthenticated remote peers can trigger the fault repeatedly by overlapping TLS handshake completion with connection close.
| Attack Vector |
Network |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:N - The flaw is in nfsd's server-side SUNRPC/TCP TLS handshake (net/sunrpc/svcsock.c), reached when a remote peer connects to port 2049 and sends a pre-authentication AUTH_TLS NULL STARTTLS probe that triggers svc_tcp_handshake() via svcauth_tls_accept().
AC:L - The attacker controls both sides of the race by initiating AUTH_TLS handshakes and concurrently resetting/closing TCP or waiting for SVC_HANDSHAKE_TO while tlshd delivers completion; repeated parallel connections make the overlap window reliably reachable.
PR:N - AUTH_TLS is processed on RPC procedure 0 before credentials are verified, so an unauthenticated remote client can reach svc_tcp_handshake() and the asynchronous callback without any account, export access, or kernel capability.
UI:N - nfsd worker threads automatically accept the TCP connection, process the STARTTLS probe, run the TLS handshake, and handle teardown/completion callbacks without any local user or administrator action.
S:U - Exploitation corrupts kernel memory on the NFS server host itself and does not cross a VM-guest/host, sandbox, or IOMMU security boundary; impact stays within the kernel's security authority.
C:H - svc_tcp_handshake_done() use-after-frees svc_sock and performs set_bit/clear_bit RMW on freed xpt_flags plus complete_all() on freed sk_handshake_done, a slab-corruption UAF that can disclose arbitrary kernel memory.
I:H - The same UAF delivers attacker-timed writes into reclaimed slab slots through atomic bit operations and wait-queue list updates, enabling heap grooming and further kernel memory corruption for arbitrary modification or code execution.
A:H - Slab corruption and UAF during handshake completion can cause kernel oops/panic, and unauthenticated remote peers can trigger the fault repeatedly by overlapping TLS handshake completion with connection close.
CVSS 3.1