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[83.28.36.208]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-560827a020dsm530210e87.118.2025.09.02.02.07.34 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Tue, 02 Sep 2025 02:07:34 -0700 (PDT) Date: Tue, 2 Sep 2025 11:07:30 +0200 From: =?UTF-8?B?TWljaGHFgg==?= Pecio To: "David Wang" <00107082@163.com> Cc: "Mathias Nyman" , WeitaoWang-oc@zhaoxin.com, gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, regressions@lists.linux.dev, linux-kernel@vger.kernel.org, surenb@google.com, kent.overstreet@linux.dev Subject: Re: [PATCH] usb: xhci: Fix xhci_free_virt_devices_depth_first() Message-ID: <20250902110730.723a48a0.michal.pecio@gmail.com> In-Reply-To: <20250902104630.6a9f088a.michal.pecio@gmail.com> References: <20250829181354.4450-1-00107082@163.com> <20250830114828.3dd8ed56.michal.pecio@gmail.com> <5051e27a.2ba3.198fa7b5f31.Coremail.00107082@163.com> <20250902093017.13d6c666.michal.pecio@gmail.com> <446082a4.7dbe.199098cd654.Coremail.00107082@163.com> <20250902104630.6a9f088a.michal.pecio@gmail.com> Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Tue, 2 Sep 2025 10:46:30 +0200, Micha=C5=82 Pecio wrote: > On Tue, 2 Sep 2025 16:30:48 +0800 (CST), David Wang wrote: > > About the change from "<" to "<=3D", I did not observe any difference o= n my system. Is it because my system does not use up all slots? =20 >=20 > This too, you would need to fiddle with devices (or connect enough > of them) to reach Slot ID 255 (probably the highest on most systems), > depending on the xHCI controller and its ID allocation policy. This made me wonder what those policies are. I'm too lazy for thorough testing, but I plugged and unplugged the same device a few times. Most HCs kept assigning ID 1, so they likely always pick the lowest. My AMD chipset, two ASMedia USB 3.1 controllers and a Fresco FL1100 kept assigning sequentially increasing IDs, so I suppose I could pump it up near the top, connect two high speed hubs and trigger this bug. > But also as explained, this bug doesn't make things go boom just yet. >=20 > Except if combined with your bug in an obscure edge case: >=20 > 1. A high speed hub has slot ID HCS_MAX_SLOTS-1 and some TT children. > 2. Another high speed hub has slot ID HCS_MAX_SLOTS. > 3. We start with freeing the second hub. > 4. The loop is entered and leaves vdev pointing at the first hub. > 5. The first hub is freed instead of the second one. > 6. Then its children are freed and UAF its tt_info.