From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8E4E93537FC; Wed, 8 Apr 2026 18:17:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775672273; cv=none; b=BfZOhihXy6OKVzha9zFYnPlmnhyL3+KlP6SVUXYGfh2oVcsRqkvNloV5GkGouA6ZzJPE7Ip7qTnrDYgvAVsxStLpPnGu70vrsb4Rmd9cbymAIgO1cD+vWjFh1nunWHQQCD72++tZ6v8dbW7OY4jZx5FKjE3V0y3lULkovQA6dzQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775672273; c=relaxed/simple; bh=F/97+6CanWAGssZ74JTlCm54BCw6kJ+k9a+Uuj0kT4U=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YhX/1A4eVkCWx2aySQGEKmjWaIZ1/Cu4bUnBXoeXWWqYJ8Myrzj667dlCpKYjQt3qXdY5HyDDhbCneVnyHoYfpFcfetiCoCqV4dmf+n+oYnb+6EFqFEPwVeWDPgyYvaZg7Ny+o0MjKIbcPSHRiFeizmgIJYE92lRmCk8+lhR49w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=rqyEb9b0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="rqyEb9b0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F0973C19421; Wed, 8 Apr 2026 18:17:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1775672273; bh=F/97+6CanWAGssZ74JTlCm54BCw6kJ+k9a+Uuj0kT4U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rqyEb9b0WOv/WZAa0ZgFTh1XKJrtbyION/hkW273oEfBUhYx6AjUxG7sTUf89TDu3 vPNzh3LP8yv4zlrYoSDoEedW0Ojw0COYXU3q/8W9Gj27zdaxjKa4inoAp5juEeJddV 69NmVrNQqTv4N/PyYyTFU6yhp4KPDihGocUGdVIs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alan Stern , syzbot+19bed92c97bee999e5db@syzkaller.appspotmail.com, stable Subject: [PATCH 6.1 255/312] USB: dummy-hcd: Fix locking/synchronization error Date: Wed, 8 Apr 2026 20:02:52 +0200 Message-ID: <20260408175943.271830069@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260408175933.715315542@linuxfoundation.org> References: <20260408175933.715315542@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alan Stern commit 616a63ff495df12863692ab3f9f7b84e3fa7a66d upstream. Syzbot testing was able to provoke an addressing exception and crash in the usb_gadget_udc_reset() routine in drivers/usb/gadgets/udc/core.c, resulting from the fact that the routine was called with a second ("driver") argument of NULL. The bad caller was set_link_state() in dummy_hcd.c, and the problem arose because of a race between a USB reset and driver unbind. These sorts of races were not supposed to be possible; commit 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change"), along with a few followup commits, was written specifically to prevent them. As it turns out, there are (at least) two errors remaining in the code. Another patch will address the second error; this one is concerned with the first. The error responsible for the syzbot crash occurred because the stop_activity() routine will sometimes drop and then re-acquire the dum->lock spinlock. A call to stop_activity() occurs in set_link_state() when handling an emulated USB reset, after the test of dum->ints_enabled and before the increment of dum->callback_usage. This allowed another thread (doing a driver unbind) to sneak in and grab the spinlock, and then clear dum->ints_enabled and dum->driver. Normally this other thread would have to wait for dum->callback_usage to go down to 0 before it would clear dum->driver, but in this case it didn't have to wait since dum->callback_usage had not yet been incremented. The fix is to increment dum->callback_usage _before_ calling stop_activity() instead of after. Then the thread doing the unbind will not clear dum->driver until after the call to usb_gadget_udc_reset() safely returns and dum->callback_usage has been decremented again. Signed-off-by: Alan Stern Reported-by: syzbot+19bed92c97bee999e5db@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-usb/68fc7c9c.050a0220.346f24.023c.GAE@google.com/ Tested-by: syzbot+19bed92c97bee999e5db@syzkaller.appspotmail.com Fixes: 7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change") Cc: stable Link: https://patch.msgid.link/46135f42-fdbe-46b5-aac0-6ca70492af15@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/udc/dummy_hcd.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/drivers/usb/gadget/udc/dummy_hcd.c +++ b/drivers/usb/gadget/udc/dummy_hcd.c @@ -461,8 +461,13 @@ static void set_link_state(struct dummy_ /* Report reset and disconnect events to the driver */ if (dum->ints_enabled && (disconnect || reset)) { - stop_activity(dum); ++dum->callback_usage; + /* + * stop_activity() can drop dum->lock, so it must + * not come between the dum->ints_enabled test + * and the ++dum->callback_usage. + */ + stop_activity(dum); spin_unlock(&dum->lock); if (reset) usb_gadget_udc_reset(&dum->gadget, dum->driver);