usb: xhci_plat_remove: avoid NULL dereference

Since commit 4736ebd7fc ("usb: host:
xhci-plat: omit shared hcd if either root hub has no ports")
xhci->shared_hcd can be NULL, which causes the following Oops
on reboot:

[  710.124450] systemd-shutdown[1]: Rebooting.
[  710.298861] xhci-hcd xhci-hcd.2.auto: remove, state 4
[  710.304217] usb usb3: USB disconnect, device number 1
[  710.317441] xhci-hcd xhci-hcd.2.auto: USB bus 3 deregistered
[  710.323280] xhci-hcd xhci-hcd.2.auto: remove, state 1
[  710.328401] usb usb2: USB disconnect, device number 1
[  710.333515] usb 2-3: USB disconnect, device number 2
[  710.467649] xhci-hcd xhci-hcd.2.auto: USB bus 2 deregistered
[  710.475450] Unable to handle kernel NULL pointer dereference at virtual address 00000000000003b8
[  710.484425] Mem abort info:
[  710.487265]   ESR = 0x0000000096000004
[  710.491060]   EC = 0x25: DABT (current EL), IL = 32 bits
[  710.496427]   SET = 0, FnV = 0
[  710.499525]   EA = 0, S1PTW = 0
[  710.502716]   FSC = 0x04: level 0 translation fault
[  710.507648] Data abort info:
[  710.510577]   ISV = 0, ISS = 0x00000004
[  710.514462]   CM = 0, WnR = 0
[  710.517480] user pgtable: 4k pages, 48-bit VAs, pgdp=00000008b0050000
[  710.523976] [00000000000003b8] pgd=0000000000000000, p4d=0000000000000000
[  710.530961] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[  710.536551] Modules linked in: rfkill input_leds snd_soc_simple_card snd_soc_simple_card_utils snd_soc_nau8822 designware_i2s snd_soc_core dw_hdmi_ahb_audio snd_pcm_dmaengine arm_ccn panfrost ac97_bus gpu_sched snd_pcm at24 fuse configfs sdhci_of_dwcmshc sdhci_pltfm sdhci nvme led_class mmc_core nvme_core bt1_pvt polynomial tp_serio snd_seq_midi snd_seq_midi_event snd_seq snd_timer snd_rawmidi snd_seq_device snd soundcore efivarfs ipv6
[  710.575286] CPU: 7 PID: 1 Comm: systemd-shutdow Not tainted 5.19.0-rc7-00043-gfd8619f4fd54 #1
[  710.583822] Hardware name: T-Platforms TF307-MB/BM1BM1-A, BIOS 5.6 07/06/2022
[  710.590972] pstate: 40000005 (nZcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[  710.597949] pc : usb_remove_hcd+0x34/0x1e4
[  710.602067] lr : xhci_plat_remove+0x74/0x140
[  710.606351] sp : ffff800009f3b7c0
[  710.609674] x29: ffff800009f3b7c0 x28: ffff000800960040 x27: 0000000000000000
[  710.616833] x26: ffff800008dc22a0 x25: 0000000000000000 x24: 0000000000000000
[  710.623992] x23: 0000000000000000 x22: ffff000805465810 x21: ffff000805465800
[  710.631149] x20: ffff000800f80000 x19: 0000000000000000 x18: ffffffffffffffff
[  710.638307] x17: ffff000805096000 x16: ffff00080633b800 x15: ffff000806537a1c
[  710.645465] x14: 0000000000000001 x13: 0000000000000000 x12: ffff00080378d6f0
[  710.652621] x11: ffff00080041a900 x10: ffff800009b204e8 x9 : ffff8000088abaa4
[  710.659779] x8 : ffff000800960040 x7 : ffff800009409000 x6 : 0000000000000001
[  710.666936] x5 : ffff800009241000 x4 : ffff800009241440 x3 : 0000000000000000
[  710.674094] x2 : ffff000800960040 x1 : ffff000800960040 x0 : 0000000000000000
[  710.681251] Call trace:
[  710.683704]  usb_remove_hcd+0x34/0x1e4
[  710.687467]  xhci_plat_remove+0x74/0x140
[  710.691400]  platform_remove+0x34/0x70
[  710.695165]  device_remove+0x54/0x90
[  710.698753]  device_release_driver_internal+0x200/0x270
[  710.703992]  device_release_driver+0x24/0x30
[  710.708273]  bus_remove_device+0xe0/0x16c
[  710.712293]  device_del+0x178/0x390
[  710.715797]  platform_device_del.part.0+0x24/0x90
[  710.720514]  platform_device_unregister+0x30/0x50
[  710.725232]  dwc3_host_exit+0x20/0x30
[  710.728907]  dwc3_remove+0x174/0x1b0
[  710.732494]  platform_remove+0x34/0x70
[  710.736254]  device_remove+0x54/0x90
[  710.739840]  device_release_driver_internal+0x200/0x270
[  710.745078]  device_release_driver+0x24/0x30
[  710.749359]  bus_remove_device+0xe0/0x16c
[  710.753380]  device_del+0x178/0x390
[  710.756881]  platform_device_del.part.0+0x24/0x90
[  710.761598]  platform_device_unregister+0x30/0x50
[  710.766314]  of_platform_device_destroy+0xe8/0x100
[  710.771119]  device_for_each_child_reverse+0x70/0xc0
[  710.776099]  of_platform_depopulate+0x48/0x90
[  710.780468]  __dwc3_of_simple_teardown+0x28/0xe0
[  710.785099]  dwc3_of_simple_shutdown+0x20/0x30
[  710.789555]  platform_shutdown+0x30/0x40
[  710.793490]  device_shutdown+0x138/0x32c
[  710.797425]  __do_sys_reboot+0x1c4/0x2ac
[  710.801362]  __arm64_sys_reboot+0x30/0x40
[  710.805383]  invoke_syscall+0x50/0x120
[  710.809146]  el0_svc_common.constprop.0+0x68/0x124
[  710.813950]  do_el0_svc+0x3c/0xcc
[  710.817275]  el0_svc+0x60/0x12c
[  710.820428]  el0t_64_sync_handler+0xc0/0x13c
[  710.824710]  el0t_64_sync+0x18c/0x190
[  710.828386] Code: a9025bf5 f942c420 f9001fe0 d2800000 (b943ba62)
[  710.834498] ---[ end trace 0000000000000000 ]---
[  710.875958] pstore: crypto_comp_compress failed, ret = -22!
[  710.895047] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
[  710.902757] Kernel Offset: disabled
[  710.906255] CPU features: 0x800,00004811,00001082
[  710.910971] Memory Limit: none
[  710.927474] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---

To avoid the problem check for NULL in usb_remove_hcd.

Fixes: 4736ebd7fc ("usb: host: xhci-plat: omit shared hcd if either root hub has no ports")
Signed-off-by: Alexey Sheplyakov <asheplyakov@basealt.ru>
Link: https://lore.kernel.org/r/20220722141700.1271439-1-asheplyakov@basealt.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hcd.c

@@ -3033,9 +3033,15 @@ EXPORT_SYMBOL_GPL(usb_add_hcd);
  */
 void usb_remove_hcd(struct usb_hcd *hcd)
 {
-	struct usb_device *rhdev = hcd->self.root_hub;
+	struct usb_device *rhdev;
 	bool rh_registered;
 
+	if (!hcd) {
+		pr_debug("%s: hcd is NULL\n", __func__);
+		return;
+	}
+	rhdev = hcd->self.root_hub;
+
 	dev_info(hcd->self.controller, "remove, state %x\n", hcd->state);
 
 	usb_get_dev(rhdev);