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

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netdev_uses_dsa_currently() variants which better reflect the uselessness of the function's return value, which becomes outdated right after the call.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.