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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , bcm-kernel-feedback-list@broadcom.com, netdev@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH net v2] vsock/vmci: fix UAF when peer resets connection during handshake Date: Tue, 12 May 2026 09:58:51 +0700 Message-ID: <20260512025851.189140-1-minhnguyen.080505@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vmci_transport_recv_connecting_server() jumps to its destroy: label and performs an unconditional sock_put(pending) to release the explicit sock_hold() taken by vmci_transport_recv_listen() before schedule_delayed_work(). The existing comment claimed this was safe because the listen handler removes pending from the pending list on the way out, which would prevent vsock_pending_work() from dropping the same reference later. That assumption breaks for a peer RST. The default arm of the packet switch sets: err = pkt->type == VMCI_TRANSPORT_PACKET_TYPE_RST ? 0 : -EINVAL; and vmci_transport_recv_listen() only calls vsock_remove_pending() when err < 0: if (err < 0) vsock_remove_pending(sk, pending); For RST (err == 0) the socket stays on the pending list, so when vsock_pending_work() fires it takes the is_pending=true path and drops all three references itself: the pending-list reference via vsock_remove_pending(), then the two trailing sock_put(sk) calls. The unconditional sock_put() in destroy: had already dropped the explicit sock_hold() reference, so the second trailing sock_put(sk) in vsock_pending_work() is a write into the freed AF_VSOCK slab object. KASAN reports a slab-use-after-free write of 4 bytes from refcount_warn_saturate() on the workqueue path: BUG: KASAN: slab-use-after-free in refcount_warn_saturate Write of size 4 at addr ffff88800b1cac80 by task kworker Workqueue: events vsock_pending_work Call Trace: refcount_warn_saturate vsock_pending_work process_one_work worker_thread Triggering the bug requires only the ability to open a VSOCK connection to the target and send a RST before the listener accepts. Skip the sock_put() in destroy: when err == 0 so it only compensates the cases where vmci_transport_recv_listen() actually calls vsock_remove_pending(). RST is the only path that reaches destroy: with err == 0; every other path produces a negative value, so their behaviour is unchanged. Verified on lts-6.12.79 with KASAN enabled (CONFIG_KASAN_INLINE=y, kasan_multi_shot): same trigger binary, same VM, 100 iterations: without this patch 52 KASAN slab-use-after-free reports fire; with this patch applied, 0 reports. Fixes: d021c344051a ("VSOCK: Introduce VM Sockets") Cc: stable@vger.kernel.org Signed-off-by: Minh Nguyen Assisted-by: Claude:claude-opus-4-7 --- v2: - Resubmit to netdev per Stefano Garzarella's request after v1 review. - Retested the PoC with the patch applied on lts-6.12.79 with KASAN enabled: 52/100 unpatched -> 0/100 patched (same trigger binary, same VM, 100 iterations); test summary captured in the commit message. - Changed Cc: stable@kernel.org -> stable@vger.kernel.org now that the bug is no longer embargoed. - Rebased onto net/main (no functional change to the diff). v1 was sent to security@kernel.org on 2026-05-10 (not on lore archives; no public link available). v1 review summary, for reference: - Stefano Garzarella (vsock maintainer): "Overall LGTM, but I'd wait vmware guys on this that know this code better." Asked for retest and resubmission via the net tree workflow. - Bryan Tan (VMCI maintainer): "Thanks for the fix, it looks good to me." Also noted that no modern VMware product allows guest-to-guest VMCI communication, so the practical attack surface is host -> guest. net/vmw_vsock/vmci_transport.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c index 4296ca1..88d7128 100644 --- a/net/vmw_vsock/vmci_transport.c +++ b/net/vmw_vsock/vmci_transport.c @@ -1269,14 +1269,16 @@ vmci_transport_recv_connecting_server(struct sock *listener, destroy: pending->sk_err = skerr; pending->sk_state = TCP_CLOSE; - /* As long as we drop our reference, all necessary cleanup will handle - * when the cleanup function drops its reference and our destruct - * implementation is called. Note that since the listen handler will - * remove pending from the pending list upon our failure, the cleanup - * function won't drop the additional reference, which is why we do it - * here. + /* Drop the reference taken by vmci_transport_recv_listen() before + * schedule_delayed_work() only on real errors. For a peer RST + * (err == 0) the listener leaves pending on the pending list, and + * vsock_pending_work() will drop that reference itself when it + * later cleans the socket up. Calling sock_put() here in that + * case would be a double-put and free the socket while + * vsock_pending_work() still holds it. */ - sock_put(pending); + if (err < 0) + sock_put(pending); return err; } base-commit: be48e5fe51a5864566307998286a699d6b986934 -- 2.54.0