Re: [PATCH] um: vector: fix NULL pointer derefs in queue-less transports

[Anton Ivanov <anton.ivanov@cambridgegreys.com>]

On 10/04/2026 21:30, Michael Bommarito wrote:
> TAP transport sets neither VECTOR_RX nor VECTOR_TX, so
> vector_net_open() never allocates rx_queue or tx_queue.  HYBRID sets
> VECTOR_RX but not VECTOR_TX, so tx_queue is NULL there too.
>
> vector_reset_stats(), vector_poll(), vector_get_ethtool_stats(), and
> vector_get_ringparam() unconditionally deref these queue pointers,
> causing a NULL pointer crash on SMP or with any lock debugging option.
>
> Guard all queue pointer accesses with NULL checks.
>
> Fixes: 49da7e64f33e ("High Performance UML Vector Network Driver")
> Cc: stable@vger.kernel.org
> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
> Assisted-by: Claude:claude-opus-4-6
> Assisted-by: Codex:gpt-5-4
> Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
> ---
> Found while enabling KCOV and lockdep on UML for a network-stack
> test lab.  Tested boot with SMP=y + PROVE_LOCKING + DEBUG_SPINLOCK +
> DEBUG_LOCK_ALLOC + LOCKDEP + KCOV, all with vec0:transport=tap.
>
> Without the fix, the same config panics at addr 0x18 (SMP, no debug),
> 0x1c (DEBUG_SPINLOCK), or 0x30 (lockdep) -- all offsets into a NULL
> vector_queue pointer.
>
>   arch/um/drivers/vector_kern.c | 48 +++++++++++++++++------------------
>   1 file changed, 24 insertions(+), 24 deletions(-)
>
> diff --git a/arch/um/drivers/vector_kern.c b/arch/um/drivers/vector_kern.c
> index 2cc90055499a5..6134c376e57be 100644
> --- a/arch/um/drivers/vector_kern.c
> +++ b/arch/um/drivers/vector_kern.c
> @@ -105,25 +105,18 @@ static const struct {
>   
>   static void vector_reset_stats(struct vector_private *vp)
>   {
> -	/* We reuse the existing queue locks for stats */
> -
> -	/* RX stats are modified with RX head_lock held
> -	 * in vector_poll.
> -	 */
> -
> -	spin_lock(&vp->rx_queue->head_lock);
> +	if (vp->rx_queue)
> +		spin_lock(&vp->rx_queue->head_lock);
>   	vp->estats.rx_queue_max = 0;
>   	vp->estats.rx_queue_running_average = 0;
>   	vp->estats.rx_encaps_errors = 0;
>   	vp->estats.sg_ok = 0;
>   	vp->estats.sg_linearized = 0;
> -	spin_unlock(&vp->rx_queue->head_lock);
> -
> -	/* TX stats are modified with TX head_lock held
> -	 * in vector_send.
> -	 */
> +	if (vp->rx_queue)
> +		spin_unlock(&vp->rx_queue->head_lock);
>   
> -	spin_lock(&vp->tx_queue->head_lock);
> +	if (vp->tx_queue)
> +		spin_lock(&vp->tx_queue->head_lock);
>   	vp->estats.tx_timeout_count = 0;
>   	vp->estats.tx_restart_queue = 0;
>   	vp->estats.tx_kicks = 0;
> @@ -131,7 +124,8 @@ static void vector_reset_stats(struct vector_private *vp)
>   	vp->estats.tx_flow_control_xoff = 0;
>   	vp->estats.tx_queue_max = 0;
>   	vp->estats.tx_queue_running_average = 0;
> -	spin_unlock(&vp->tx_queue->head_lock);
> +	if (vp->tx_queue)
> +		spin_unlock(&vp->tx_queue->head_lock);
>   }
>   
>   static int get_mtu(struct arglist *def)
> @@ -1163,7 +1157,8 @@ static int vector_poll(struct napi_struct *napi, int budget)
>   
>   	if ((vp->options & VECTOR_TX) != 0)
>   		tx_enqueued = (vector_send(vp->tx_queue) > 0);
> -	spin_lock(&vp->rx_queue->head_lock);
> +	if (vp->rx_queue)
> +		spin_lock(&vp->rx_queue->head_lock);
>   	if ((vp->options & VECTOR_RX) > 0)
>   		err = vector_mmsg_rx(vp, budget);
>   	else {
> @@ -1171,7 +1166,8 @@ static int vector_poll(struct napi_struct *napi, int budget)
>   		if (err > 0)
>   			err = 1;
>   	}
> -	spin_unlock(&vp->rx_queue->head_lock);
> +	if (vp->rx_queue)
> +		spin_unlock(&vp->rx_queue->head_lock);
>   	if (err > 0)
>   		work_done += err;
>   
> @@ -1421,10 +1417,10 @@ static void vector_get_ringparam(struct net_device *netdev,
>   {
>   	struct vector_private *vp = netdev_priv(netdev);
>   
> -	ring->rx_max_pending = vp->rx_queue->max_depth;
> -	ring->tx_max_pending = vp->tx_queue->max_depth;
> -	ring->rx_pending = vp->rx_queue->max_depth;
> -	ring->tx_pending = vp->tx_queue->max_depth;
> +	ring->rx_max_pending = vp->rx_queue ? vp->rx_queue->max_depth : 0;
> +	ring->tx_max_pending = vp->tx_queue ? vp->tx_queue->max_depth : 0;
> +	ring->rx_pending = ring->rx_max_pending;
> +	ring->tx_pending = ring->tx_max_pending;
>   }
>   
>   static void vector_get_strings(struct net_device *dev, u32 stringset, u8 *buf)
> @@ -1466,11 +1462,15 @@ static void vector_get_ethtool_stats(struct net_device *dev,
>   	 * to date.
>   	 */
>   
> -	spin_lock(&vp->tx_queue->head_lock);
> -	spin_lock(&vp->rx_queue->head_lock);
> +	if (vp->tx_queue)
> +		spin_lock(&vp->tx_queue->head_lock);
> +	if (vp->rx_queue)
> +		spin_lock(&vp->rx_queue->head_lock);
>   	memcpy(tmp_stats, &vp->estats, sizeof(struct vector_estats));
> -	spin_unlock(&vp->rx_queue->head_lock);
> -	spin_unlock(&vp->tx_queue->head_lock);
> +	if (vp->rx_queue)
> +		spin_unlock(&vp->rx_queue->head_lock);
> +	if (vp->tx_queue)
> +		spin_unlock(&vp->tx_queue->head_lock);
>   }
>   
>   static int vector_get_coalesce(struct net_device *netdev,

Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>

-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661