Re: [PATCH 1/2] net: dsa: RCU-protect dsa_ptr in struct net_device

[Florian Fainelli <florian.fainelli@broadcom.com>]

On 9/10/24 06:03, 'A. Sverdlin' via BCM-KERNEL-FEEDBACK-LIST,PDL wrote:
> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> 
> There are multiple races of zeroing dsa_ptr in struct net_device (on
> shutdown/remove) against asynchronous dereferences all over the net
> code. Widespread pattern is as follows:
> 
> CPU0					CPU1
> if (netdev_uses_dsa())
> 					dev->dsa_ptr = NULL;
>          dev->dsa_ptr->...
> 
> One of the possible crashes:
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
> CPU: 0 PID: 12 Comm: ksoftirqd/0 Tainted: G O 6.1.99+ #1
> pc : lan9303_rcv
> lr : lan9303_rcv
> Call trace:
>   lan9303_rcv
>   dsa_switch_rcv
>   __netif_receive_skb_list_core
>   netif_receive_skb_list_internal
>   napi_gro_receive
>   fec_enet_rx_napi
>   __napi_poll
>   net_rx_action
> ...
> 
> RCU-protect dsa_ptr and use rcu_dereference() or rtnl_dereference()
> depending on the calling context.
> 
> Rename netdev_uses_dsa() into __netdev_uses_dsa_currently()
> (assumes ether RCU or RTNL lock held) and netdev_uses_dsa_currently()
> variants which better reflect the uselessness of the function's
> return value, which becomes outdated right after the call.
> 
> Fixes: ee534378f005 ("net: dsa: fix panic when DSA master device unbinds on shutdown")
> Cc: stable@vger.kernel.org
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Thanks for doing this work, just a few nits below. This is likely to be 
difficult to backport to stable trees.

> ---
>   drivers/net/dsa/mt7530.c                    |   3 +-
>   drivers/net/dsa/ocelot/felix.c              |   3 +-
>   drivers/net/dsa/qca/qca8k-8xxx.c            |   3 +-
>   drivers/net/ethernet/broadcom/bcmsysport.c  |   8 +-
>   drivers/net/ethernet/mediatek/airoha_eth.c  |   2 +-
>   drivers/net/ethernet/mediatek/mtk_eth_soc.c |  22 +++--
>   drivers/net/ethernet/mediatek/mtk_ppe.c     |  15 ++-
>   include/linux/netdevice.h                   |   2 +-
>   include/net/dsa.h                           |  36 +++++--
>   include/net/dsa_stubs.h                     |   6 +-
>   net/bridge/br_input.c                       |   2 +-
>   net/core/dev.c                              |   3 +-
>   net/core/flow_dissector.c                   |  19 ++--
>   net/dsa/conduit.c                           |  66 ++++++++-----
>   net/dsa/dsa.c                               |  19 ++--
>   net/dsa/port.c                              |   3 +-
>   net/dsa/tag.c                               |   3 +-
>   net/dsa/tag.h                               |  19 ++--
>   net/dsa/tag_8021q.c                         |  10 +-
>   net/dsa/tag_brcm.c                          |   2 +-
>   net/dsa/tag_dsa.c                           |   8 +-
>   net/dsa/tag_qca.c                           |  10 +-
>   net/dsa/tag_sja1105.c                       |  22 +++--
>   net/dsa/user.c                              | 104 +++++++++++---------
>   net/ethernet/eth.c                          |   2 +-
>   25 files changed, 240 insertions(+), 152 deletions(-)
> 
> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> index ec18e68bf3a8..82d3f1786156 100644
> --- a/drivers/net/dsa/mt7530.c
> +++ b/drivers/net/dsa/mt7530.c
> @@ -20,6 +20,7 @@
>   #include <linux/reset.h>
>   #include <linux/gpio/consumer.h>
>   #include <linux/gpio/driver.h>
> +#include <linux/rtnetlink.h>
>   #include <net/dsa.h>
>   
>   #include "mt7530.h"
> @@ -3092,7 +3093,7 @@ mt753x_conduit_state_change(struct dsa_switch *ds,
>   			    const struct net_device *conduit,
>   			    bool operational)
>   {
> -	struct dsa_port *cpu_dp = conduit->dsa_ptr;
> +	struct dsa_port *cpu_dp = rtnl_dereference(conduit->dsa_ptr);

Out of curiosity, only sparse will likely be able to recognize the __rcu 
annotation of net_device::dsa_ptr so there is still unfortunately room 
for programmers to forget about using rtnl_dereference(), this should 
hopefully be caught by CI when patches are submitted.

>   	struct mt7530_priv *priv = ds->priv;
>   	int val = 0;
>   	u8 mask;
> diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
> index 4a705f7333f4..f6bc0ff0c116 100644
> --- a/drivers/net/dsa/ocelot/felix.c
> +++ b/drivers/net/dsa/ocelot/felix.c
> @@ -21,6 +21,7 @@
>   #include <linux/of_net.h>
>   #include <linux/pci.h>
>   #include <linux/of.h>
> +#include <linux/rtnetlink.h>
>   #include <net/pkt_sched.h>
>   #include <net/dsa.h>
>   #include "felix.h"
> @@ -57,7 +58,7 @@ static int felix_cpu_port_for_conduit(struct dsa_switch *ds,
>   		return lag;
>   	}
>   
> -	cpu_dp = conduit->dsa_ptr;
> +	cpu_dp = rtnl_dereference(conduit->dsa_ptr);
>   	return cpu_dp->index;
>   }
>   
> diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
> index f8d8c70642c4..10b4d7e9be2f 100644
> --- a/drivers/net/dsa/qca/qca8k-8xxx.c
> +++ b/drivers/net/dsa/qca/qca8k-8xxx.c
> @@ -20,6 +20,7 @@
>   #include <linux/gpio/consumer.h>
>   #include <linux/etherdevice.h>
>   #include <linux/dsa/tag_qca.h>
> +#include <linux/rtnetlink.h>
>   
>   #include "qca8k.h"
>   #include "qca8k_leds.h"
> @@ -1754,7 +1755,7 @@ static void
>   qca8k_conduit_change(struct dsa_switch *ds, const struct net_device *conduit,
>   		     bool operational)
>   {
> -	struct dsa_port *dp = conduit->dsa_ptr;
> +	struct dsa_port *dp = rtnl_dereference(conduit->dsa_ptr);
>   	struct qca8k_priv *priv = ds->priv;
>   
>   	/* Ethernet MIB/MDIO is only supported for CPU port 0 */
> diff --git a/drivers/net/ethernet/broadcom/bcmsysport.c b/drivers/net/ethernet/broadcom/bcmsysport.c
> index c9faa8540859..bd9bc081346d 100644
> --- a/drivers/net/ethernet/broadcom/bcmsysport.c
> +++ b/drivers/net/ethernet/broadcom/bcmsysport.c
> @@ -145,7 +145,7 @@ static void bcm_sysport_set_rx_csum(struct net_device *dev,
>   	 * sure we tell the RXCHK hardware to expect a 4-bytes Broadcom
>   	 * tag after the Ethernet MAC Source Address.
>   	 */
> -	if (netdev_uses_dsa(dev))
> +	if (__netdev_uses_dsa_currently(dev))

I appreciate the thought given into the function name, though I am not 
sure it is warranted to suffix with _currently().

>   		reg |= RXCHK_BRCM_TAG_EN;
>   	else
>   		reg &= ~RXCHK_BRCM_TAG_EN;
> @@ -173,7 +173,7 @@ static void bcm_sysport_set_tx_csum(struct net_device *dev,
>   	 * checksum to be computed correctly when using VLAN HW acceleration,
>   	 * else it has no effect, so it can always be turned on.
>   	 */
> -	if (netdev_uses_dsa(dev))
> +	if (__netdev_uses_dsa_currently(dev))
>   		reg |= tdma_control_bit(priv, SW_BRCM_TAG);
>   	else
>   		reg &= ~tdma_control_bit(priv, SW_BRCM_TAG);
> @@ -1950,7 +1950,7 @@ static inline void gib_set_pad_extension(struct bcm_sysport_priv *priv)
>   
>   	reg = gib_readl(priv, GIB_CONTROL);
>   	/* Include Broadcom tag in pad extension and fix up IPG_LENGTH */
> -	if (netdev_uses_dsa(priv->netdev)) {
> +	if (__netdev_uses_dsa_currently(priv->netdev)) {
>   		reg &= ~(GIB_PAD_EXTENSION_MASK << GIB_PAD_EXTENSION_SHIFT);
>   		reg |= ENET_BRCM_TAG_LEN << GIB_PAD_EXTENSION_SHIFT;
>   	}
> @@ -2299,7 +2299,7 @@ static u16 bcm_sysport_select_queue(struct net_device *dev, struct sk_buff *skb,
>   	struct bcm_sysport_tx_ring *tx_ring;
>   	unsigned int q, port;
>   
> -	if (!netdev_uses_dsa(dev))
> +	if (!__netdev_uses_dsa_currently(dev))
>   		return netdev_pick_tx(dev, skb, NULL);
>   
>   	/* DSA tagging layer will have configured the correct queue */
> diff --git a/drivers/net/ethernet/mediatek/airoha_eth.c b/drivers/net/ethernet/mediatek/airoha_eth.c
> index 1c5b85a86df1..f7425d393b22 100644
> --- a/drivers/net/ethernet/mediatek/airoha_eth.c
> +++ b/drivers/net/ethernet/mediatek/airoha_eth.c
> @@ -2255,7 +2255,7 @@ static int airoha_dev_open(struct net_device *dev)
>   	if (err)
>   		return err;
>   
> -	if (netdev_uses_dsa(dev))
> +	if (__netdev_uses_dsa_currently(dev))
>   		airoha_fe_set(eth, REG_GDM_INGRESS_CFG(port->id),
>   			      GDM_STAG_EN_MASK);
>   	else
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index 16ca427cf4c3..82a828349323 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -24,6 +24,7 @@
>   #include <linux/pcs/pcs-mtk-lynxi.h>
>   #include <linux/jhash.h>
>   #include <linux/bitfield.h>
> +#include <linux/rcupdate.h>
>   #include <net/dsa.h>
>   #include <net/dst_metadata.h>
>   #include <net/page_pool/helpers.h>
> @@ -1375,7 +1376,8 @@ static void mtk_tx_set_dma_desc_v2(struct net_device *dev, void *txd,
>   		/* tx checksum offload */
>   		if (info->csum)
>   			data |= TX_DMA_CHKSUM_V2;
> -		if (mtk_is_netsys_v3_or_greater(eth) && netdev_uses_dsa(dev))
> +		if (mtk_is_netsys_v3_or_greater(eth) &&
> +		    __netdev_uses_dsa_currently(dev))
>   			data |= TX_DMA_SPTAG_V3;
>   	}
>   	WRITE_ONCE(desc->txd5, data);
> @@ -2183,7 +2185,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>   		 * hardware treats the MTK special tag as a VLAN and untags it.
>   		 */
>   		if (mtk_is_netsys_v1(eth) && (trxd.rxd2 & RX_DMA_VTAG) &&
> -		    netdev_uses_dsa(netdev)) {
> +		    __netdev_uses_dsa_currently(netdev)) {
>   			unsigned int port = RX_DMA_VPID(trxd.rxd3) & GENMASK(2, 0);
>   
>   			if (port < ARRAY_SIZE(eth->dsa_meta) &&
> @@ -3304,7 +3306,7 @@ static void mtk_gdm_config(struct mtk_eth *eth, u32 id, u32 config)
>   
>   	val |= config;
>   
> -	if (eth->netdev[id] && netdev_uses_dsa(eth->netdev[id]))
> +	if (eth->netdev[id] && __netdev_uses_dsa_currently(eth->netdev[id]))
>   		val |= MTK_GDMA_SPECIAL_TAG;
>   
>   	mtk_w32(eth, val, MTK_GDMA_FWD_CFG(id));
> @@ -3313,12 +3315,16 @@ static void mtk_gdm_config(struct mtk_eth *eth, u32 id, u32 config)
>   
>   static bool mtk_uses_dsa(struct net_device *dev)
>   {
> +	bool ret = false;
>   #if IS_ENABLED(CONFIG_NET_DSA)
> -	return netdev_uses_dsa(dev) &&
> -	       dev->dsa_ptr->tag_ops->proto == DSA_TAG_PROTO_MTK;
> -#else
> -	return false;
> +	struct dsa_port *dp;
> +
> +	rcu_read_lock();
> +	dp = rcu_dereference(dev->dsa_ptr);
> +	ret = dp && dp->tag_ops->proto == DSA_TAG_PROTO_MTK;
> +	rcu_read_unlock();

This pattern repeats in mtk_ppe.c, a possible factoring for later.
-- 
Florian