vsock/vmci: fix UAF when peer resets connection during handshake

Overview

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

vsock/vmci: fix UAF when peer resets connection during handshake

vmci_transport_recv_connecting_server() returned err = 0 for a peer RST in its default switch arm:

err = pkt->type == VMCI_TRANSPORT_PACKET_TYPE_RST ? 0 : -EINVAL;

That made vmci_transport_recv_listen() skip vsock_remove_pending(), leaving the pending socket on the listener's pending_links with sk_state = TCP_CLOSE while destroy: still dropped the explicit reference taken before schedule_delayed_work().

One second later vsock_pending_work() observed is_pending=true and performed full cleanup: vsock_remove_pending() then the two trailing sock_put(sk) calls -- the first reached refcount 0 and __sk_freed the socket, and the second wrote into the freed object:

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

Treat peer RST like any other unexpected packet type (err = -EINVAL). All destroy: arms now return err < 0, so vmci_transport_recv_listen() removes pending from pending_links synchronously and vsock_pending_work() takes the is_pending=false / !rejected branch, dropping only its own work reference. This also closes the multi-packet race Sashiko reported on v2: pending is removed from the list before any subsequent packet can find it.

The pre-existing sk_acceptq_removed() gap on the err < 0 path of vmci_transport_recv_listen() that Sashiko also noted is not introduced or changed by this patch.

Tested on lts-6.12.79 with KASAN: 52/100 unpatched -> 0/100 patched.

Affected

• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < 1e19f08552b90070ed18bafb1763c78297823af6
• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < 1dd531e28f61edd286edc486ab068f135b5ae1eb
• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < ecda37f8faab3220da199335e42564cb7a9ad145
• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < cc27e989a5dfdfcfc1cca7c3be27a0c7532b46cb
• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < 47e63077605c6c2aa45b3df9847a8cdc1f1f6ef9
• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < 440447699c681e26ed58e9c309cad718270a18b4
• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < 9fe74e42914c851d68069713b7b917a9c33faf26
• Linux >= d021c344051af91f42c5ba9fdedc176740cbd238 < 99e22ddf4edb63dc8382bc028af928056d3450cf
• Linux 3.9

Remediation

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