On Tue, May 12, 2026 at 3:59 AM Minh Nguyen <[email protected]> wrote: > > 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: [email protected] > Signed-off-by: Minh Nguyen <[email protected]> > 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: [email protected] -> [email protected] now that the > bug is no longer embargoed. > - Rebased onto net/main (no functional change to the diff). > > v1 was sent to [email protected] 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(-)
Acked-by: Bryan Tan <[email protected]> > > 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 >
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