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([187.13.210.57]) by smtp.gmail.com with ESMTPSA id ada2fe7eead31-7cb3411becasm3854339137.0.2026.10.10.07.27.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 10 Oct 2026 07:27:22 -0700 (PDT) From: Aldo Ariel Panzardo To: Kuen-Han Tsai Cc: Aldo Ariel Panzardo , Greg Kroah-Hartman , Ivaylo Dimitrov , Faqiang Zhu , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 2/2] usb: gadget: u_ether: Protect dev->gadget access with dev->lock Date: Sat, 10 Oct 2026 11:27:07 -0300 Message-ID: <20261010142713.2667481-1-qwe.aldo@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260923-u-ether-gadget-npe-v1-2-ff466c55ecc0@google.com> References: <20260923-u-ether-gadget-npe-v1-2-ff466c55ecc0@google.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Wed, Sep 23, 2026 at 03:58:36PM +0800, Kuen-Han Tsai wrote: > Extend dev->lock to protect dev->gadget across gether_set_gadget(), > gether_detach_gadget(), eth_get_drvinfo(), and rx_submit(). Confirmed against mainline. The race is real: eth_get_drvinfo() runs from ethtool independently of unbind, so its NULL check and the dev->gadget->name / dev_name(&dev->gadget->dev) dereferences could race gether_detach_gadget() clearing dev->gadget. Holding dev->lock across the check and both dereferences, while gether_set_gadget() and gether_detach_gadget() now update dev->gadget under the same lock, closes it. The rest holds up too. In rx_submit() the cached g is both read and dereferenced (g->quirk_ep_out_aligned_size) inside the dev->lock section, and it is only reached when dev->port_usb != NULL; since gether_disconnect() nulls dev->port_usb and drains all I/O before any gether_detach_gadget(), a non-NULL port_usb there implies a live gadget, so g is valid. Clearing dev->gadget before device_move() in gether_detach_gadget() is fine -- nothing between the two reads dev->gadget and device_move() does not touch it. No lock inversion either: the sole rtnl section is unrelated and never nested under dev->lock, and the guarded regions only do strscpy/pointer work, so nothing sleeps under the lock. One note, not blocking: the struct comment now says the lock is held while accessing gadget, but gether_connect() and gether_register_netdev() still read dev->gadget unlocked. Those run on the set_alt()/setup path, which the composite core serializes against unbind (gether_detach_gadget() is only reached from the *_unbind callbacks), so they are safe -- the comment just reads a touch broader than what is actually enforced. Reviewed-by: Aldo Ariel Panzardo