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Message-ID: <446082a4.7dbe.199098cd654.Coremail.00107082@163.com>
Date: Tue, 2 Sep 2025 16:30:48 +0800 (CST)
From: "David Wang" <00107082@....com>
To: "Michal Pecio" <michal.pecio@...il.com>
Cc: "Mathias Nyman" <mathias.nyman@...ux.intel.com>,
WeitaoWang-oc@...oxin.com, gregkh@...uxfoundation.org,
linux-usb@...r.kernel.org, regressions@...ts.linux.dev,
linux-kernel@...r.kernel.org, surenb@...gle.com,
kent.overstreet@...ux.dev
Subject: Re:[PATCH] usb: xhci: Fix xhci_free_virt_devices_depth_first()
At 2025-09-02 15:30:17, "Michal Pecio" <michal.pecio@...il.com> wrote:
>Reusing 'vdev' for iteration caused a recent commit to malfunction
>uexpectedly, resulting in a reported memory leak and potential UAF
>if devices are freed in bad order. Using a second variable solves
>this problem, and maybe others later.
>
>HCS_MAX_SLOTS(xhci->hcs_params1) is the highest possible slot_id,
>so change the iteration range to include it. Currently this doesn't
>seem to cause problems because the only caller begins with freeing
>the topmost slot_id, but it breaks documented functionality.
>
>Reported-by: David Wang <00107082@....com>
>Closes: https://lore.kernel.org/linux-usb/20250829181354.4450-1-00107082@163.com/
>Fixes: 2eb03376151b ("usb: xhci: Fix slot_id resource race conflict")
>Fixes: ee8665e28e8d ("xhci: free xhci virtual devices with leaf nodes first")
>Cc: stable@...r.kernel.org
>Signed-off-by: Michal Pecio <michal.pecio@...il.com>
>---
> drivers/usb/host/xhci-mem.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
>index eed5926b200e..db7dc70c37e5 100644
>--- a/drivers/usb/host/xhci-mem.c
>+++ b/drivers/usb/host/xhci-mem.c
>@@ -932,7 +932,7 @@ void xhci_free_virt_device(struct xhci_hcd *xhci, struct xhci_virt_device *dev,
> */
> static void xhci_free_virt_devices_depth_first(struct xhci_hcd *xhci, int slot_id)
> {
>- struct xhci_virt_device *vdev;
>+ struct xhci_virt_device *vdev, *vdev_i;
> struct list_head *tt_list_head;
> struct xhci_tt_bw_info *tt_info, *next;
> int i;
>@@ -951,9 +951,9 @@ static void xhci_free_virt_devices_depth_first(struct xhci_hcd *xhci, int slot_i
> /* is this a hub device that added a tt_info to the tts list */
> if (tt_info->slot_id == slot_id) {
> /* are any devices using this tt_info? */
>- for (i = 1; i < HCS_MAX_SLOTS(xhci->hcs_params1); i++) {
>- vdev = xhci->devs[i];
>- if (vdev && (vdev->tt_info == tt_info))
>+ for (i = 1; i <= HCS_MAX_SLOTS(xhci->hcs_params1); i++) {
>+ vdev_i = xhci->devs[i];
>+ if (vdev_i && (vdev_i->tt_info == tt_info))
> xhci_free_virt_devices_depth_first(
> xhci, i);
> }
>--
>2.48.1
Tested-by: David Wang <00107082@....com>
About the change from "<" to "<=", I did not observe any difference on my system. Is it because my system does not use up all slots?
Thanks
David
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