From: Peilin Hehe.peilin@zte.com.cn

Upstream commit 6c24a03a61a2 ("net: dsa: improve shutdown sequence")

Issue ===== Repeatedly accessing the DSA Ethernet controller via the ethtool command, followed by a system reboot, may trigger a DSA null pointer dereference, causing a kernel panic and preventing the system from rebooting properly. This can lead to data loss or denial-of-service, resulting in serious consequences.

The following is the panic log: [ 172.523467] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020 [ 172.706923] Call trace: [ 172.709371] dsa_master_get_sset_count+0x24/0xa4 [ 172.714000] ethtool_get_drvinfo+0x8c/0x210 [ 172.718193] dev_ethtool+0x780/0x2120 [ 172.721863] dev_ioctl+0x1b0/0x580 [ 172.725273] sock_do_ioctl+0xc0/0x100 [ 172.728944] sock_ioctl+0x130/0x3c0 [ 172.732440] __arm64_sys_ioctl+0xb4/0x100 [ 172.736460] invoke_syscall+0x50/0x120 [ 172.740219] el0_svc_common.constprop.0+0x4c/0xf4 [ 172.744936] do_el0_svc+0x2c/0xa0 [ 172.748257] el0_svc+0x20/0x60 [ 172.751318] el0t_64_sync_handler+0xe8/0x114 [ 172.755599] el0t_64_sync+0x180/0x184 [ 172.759271] Code: a90153f3 2a0103f4 a9025bf5 f9418015 (f94012b6) [ 172.765383] ---[ end trace 0000000000000002 ]---

Root Cause ========== Based on analysis of the Linux 5.15 stable version, the function dsa_master_get_sset_count() accesses members of the structure pointed to by cpu_dp without checking for a null pointer. If cpu_dp is a null pointer, this will cause a kernel panic.

static int dsa_master_get_sset_count(struct net_device *dev, int sset) { struct dsa_port *cpu_dp = dev->dsa_ptr; const struct ethtool_ops *ops = cpu_dp->orig_ethtool_ops; struct dsa_switch *ds = cpu_dp->ds; ... }

dev->dsa_ptr is set to NULL in the dsa_switch_shutdown() or dsa_master_teardown() functions. When the DSA module unloads, dsa_master_ethtool_teardown(dev) restores the original copy of the DSA device's ethtool_ops using "dev->ethtool_ops = cpu_dp->orig_ethtool_ops;" before setting dev->dsa_ptr to NULL. This ensures that ethtool_ops remains accessible after DSA unloads. However, dsa_switch_shutdown does not restore the original copy of the DSA device's ethtool_ops, potentially leading to a null pointer dereference of dsa_ptr and causing a system panic. Essentially, when we set master->dsa_ptr to NULL, we need to ensure that no user ports are making requests to the DSA driver.

Solution ======== The addition of the netif_device_detach() function is to ensure that ioctls, rtnetlinks and ethtool requests on the user ports no longer propagate down to the driver - we're no longer prepared to handle them.

Fixes: ee534378f005 ("net: dsa: fix panic when DSA master device unbinds on shutdown") Suggested-by: Vladimir Oltean vladimir.oltean@nxp.com Signed-off-by: Peilin He he.peilin@zte.com.cn Reviewed-by: xu xin xu.xin16@zte.com.cn Signed-off-by: Kun Jiang jiang.kun2@zte.com.cn Cc: Fan Yu fan.yu9@zte.com.cn Cc: Yutan Qiu qiu.yutan@zte.com.cn Cc: Yaxin Wang wang.yaxin@zte.com.cn Cc: tuqiang tu.qiang35@zte.com.cn Cc: Yang Yang yang.yang29@zte.com.cn Cc: ye xingchen ye.xingchen@zte.com.cn Cc: Yunkai Zhang zhang.yunkai@zte.com.cn --- net/dsa/dsa2.c | 7 +++++++ 1 file changed, 7 insertions(+)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c index 543834e31298..bf384b30ec0a 100644 --- a/net/dsa/dsa2.c +++ b/net/dsa/dsa2.c @@ -1656,6 +1656,7 @@ EXPORT_SYMBOL_GPL(dsa_unregister_switch); void dsa_switch_shutdown(struct dsa_switch *ds) { struct net_device *master, *slave_dev; + LIST_HEAD(close_list); struct dsa_port *dp;

mutex_lock(&dsa2_mutex); @@ -1665,6 +1666,11 @@ void dsa_switch_shutdown(struct dsa_switch *ds)

rtnl_lock();

+ dsa_switch_for_each_cpu_port(dp, ds) + list_add(&dp->master->close_list, &close_list); + + dev_close_many(&close_list, true); + list_for_each_entry(dp, &ds->dst->ports, list) { if (dp->ds != ds) continue; @@ -1675,6 +1681,7 @@ void dsa_switch_shutdown(struct dsa_switch *ds) master = dp->cpu_dp->master; slave_dev = dp->slave;

+ netif_device_detach(slave_dev); netdev_upper_dev_unlink(master, slave_dev); }