Re: [PATCH 1/2] usb: gadget: tegra-xudc: Fix crash in vbus_draw

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On 06/04/2023 09:05, Thierry Reding wrote:
On Wed, Apr 05, 2023 at 07:18:53PM +0100, Jon Hunter wrote:
Commit ac82b56bda5f ("usb: gadget: tegra-xudc: Add vbus_draw support")
populated the vbus_draw callback for the Tegra XUDC driver. The function
tegra_xudc_gadget_vbus_draw(), that was added by this commit, assumes
that the pointer 'curr_usbphy' has been initialised, which is not always
the case because this is only initialised when the USB role is updated.
Fix this crash, by checking that the 'curr_usbphy' is valid before
dereferencing.

Fixes: ac82b56bda5f ("usb: gadget: tegra-xudc: Add vbus_draw support")
Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx>
---
  drivers/usb/gadget/udc/tegra-xudc.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/udc/tegra-xudc.c b/drivers/usb/gadget/udc/tegra-xudc.c
index 2b71b33725f1..5bccd64847ff 100644
--- a/drivers/usb/gadget/udc/tegra-xudc.c
+++ b/drivers/usb/gadget/udc/tegra-xudc.c
@@ -2167,7 +2167,7 @@ static int tegra_xudc_gadget_vbus_draw(struct usb_gadget *gadget,
dev_dbg(xudc->dev, "%s: %u mA\n", __func__, m_a); - if (xudc->curr_usbphy->chg_type == SDP_TYPE)
+	if (xudc->curr_usbphy && xudc->curr_usbphy->chg_type == SDP_TYPE)
  		ret = usb_phy_set_power(xudc->curr_usbphy, m_a);
return ret;

Looking at tegra_xudc_probe(), that calls tegra_xudc_update_data_role()
for all PHYs, so shouldn't that be enough to get curr_usbphy set? Or is
there perhaps a race between ->vbus_draw() and the data role update? Is
->vbus_draw() perhaps called as part of usb_add_gadget_udc()? Should we
reorder those to make sure the role is properly updated before the
gadget is registered?

Yes it does call it, but it still does not set the curr_usbphy. If you look at the function it may not set it.

In the backtrace I saw, which was happening on reboot, it was in the unregister of the gadget ...

[ 1102.047896] Call trace:
[ 1102.050402]  0xffffde9fd18c0878
[ 1102.053602]  usb_gadget_vbus_draw+0x28/0x50
[ 1102.057879]  composite_disconnect+0x1c/0x40 [libcomposite]
[ 1102.063509]  usb_get_function_instance+0x1808/0x27b0 [libcomposite]
[ 1102.069935]  usb_gadget_disconnect+0x64/0xa0
[ 1102.074304]  usb_gadget_remove_driver+0x2c/0xc0
[ 1102.078942]  usb_gadget_unregister_driver+0x70/0xf0
[ 1102.083927]  usb_get_function_instance+0x2774/0x27b0 [libcomposite]
[ 1102.090339]  unregister_gadget_item+0x280/0x470 [libcomposite]
[ 1102.096314]  configfs_write_iter+0xc4/0x120
[ 1102.100609]  new_sync_write+0xe8/0x190
[ 1102.104461]  vfs_write+0x234/0x380
[ 1102.107938]  ksys_write+0x6c/0x100
[ 1102.111417]  __arm64_sys_write+0x1c/0x30
[ 1102.115427]  invoke_syscall.constprop.0+0x4c/0xe0
[ 1102.120245]  do_el0_svc+0x50/0x150
[ 1102.123723]  el0_svc+0x28/0xc0
[ 1102.126854]  el0t_64_sync_handler+0xb0/0xc0
[ 1102.131138]  el0t_64_sync+0x1a0/0x1a4
[ 1102.134889] Code: 910003fd a90153f3 f94ce413 f100027f (b9409a60)
[ 1102.141139] ---[ end trace cdf6612bd43fcbf2 ]---

Jon



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