From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 839BFC636CB for ; Mon, 19 Jul 2021 09:59:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 62C366108B for ; Mon, 19 Jul 2021 09:59:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236251AbhGSJSV (ORCPT ); Mon, 19 Jul 2021 05:18:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42258 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236212AbhGSJSS (ORCPT ); Mon, 19 Jul 2021 05:18:18 -0400 Received: from mail-ed1-x530.google.com (mail-ed1-x530.google.com [IPv6:2a00:1450:4864:20::530]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8B29CC061574; Mon, 19 Jul 2021 02:02:48 -0700 (PDT) Received: by mail-ed1-x530.google.com with SMTP id ee25so23126215edb.5; Mon, 19 Jul 2021 02:58:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=FXmf8gnmrhy2GyOGMcTkKRbmrND8t8oV7ZWyl5/d3aI=; b=TjIKZrf9Ms60L2amW06L8YjtBgylgXv6ZYq5B2EZ8I0BxZBYOcdK8EF/GK9NIPUq6R 4uwzWni2FbCqBN13OxHHNO0ldPBvvPJCyNg4fF78stdHM+qvZabF5e+gcZ2c842S5WDZ i1zM4mG8cj2B3RLoOT9/T4UglMIR84LFhJ+Uudc84YrOvJuHcLOGQo5FfV0Gip49jVNC TvUbhJ0xqGlc+Mt3eRIrvxgvWBIUgQCXRa9fyJ824k8Wt/+UodS/gTBUDRk1PEJVoyxN lSF1KXDHu2AI3K7rvArATcgGH4yyMGAXGV9m/tkXyDAdLSgP3hyatkSQeWK0DSp2QtGO Az6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=FXmf8gnmrhy2GyOGMcTkKRbmrND8t8oV7ZWyl5/d3aI=; b=AQi0RWqkwJ5aNKSq3NjNLOI4Y2H2FE60a2WbJkLj88DaztNfBpqk4b7gtMkf39J7E1 9n+3f5mj9WKB4P8erERzKavA0m9AqA02AhY+cBUR8j9iahGiYgqLJ1B9A2aU2AQQ76tK cJRfbQOkHS2UaXViY+/5BIogTWfMD6lHAbEil3AV6ZSwG1Ww4+0gylwnaMcfJnCSdiqg QMuB9DOfd0jNhbwwVN71ZsWYBfvzuF0Ivxn1TCzzq1aAStydX3cAetJ3MeTeWdoH03Ow rv8Tlxy3gQt7IUK0KLNMSuQCS8m89a/pwXbBsACkSv4RNbIKvTA92bg8awkEHZlM5ioH 5now== X-Gm-Message-State: AOAM532DYzf7POOnqUQe5pM27b1FsTgeZyWms0Z38mSBFpLnBbgdgKpK i5oNHA6Iu4v6NbmcFTpKNZMCvJffjYgy4yFuYns= X-Google-Smtp-Source: ABdhPJxwgNhJ13JftchIfihnAK4wrWoUBHwunAFqMOhuCHNJS0nl2W2bClagI2IslOPYbS/sC7WBD5jtohu1jX2SDyU= X-Received: by 2002:a05:6402:4c5:: with SMTP id n5mr33082879edw.322.1626688736695; Mon, 19 Jul 2021 02:58:56 -0700 (PDT) MIME-Version: 1.0 References: <20210707093409.1445747-1-mudongliangabcd@gmail.com> <20210713084853.GA6572@gofer.mess.org> In-Reply-To: From: Dongliang Mu Date: Mon, 19 Jul 2021 17:58:30 +0800 Message-ID: Subject: Re: [PATCH v2] [media] em28xx-input: fix refcount bug in em28xx_usb_disconnect To: Sean Young Cc: Mauro Carvalho Chehab , Igor Matheus Andrade Torrente , Hans Verkuil , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 19, 2021 at 5:57 PM Dongliang Mu wrote: > > This can also fix another crash report - KASAN: use-after-free Read in > em28xx_close_extension [1]. It should be duplicated bug reports with > the memory leak. not memory leak, just the refcount bug mentioned in the commit message. > > [1] https://syzkaller.appspot.com/bug?id=a09553fd4df4c4a3824dc37a4040bf80d2600a50 > > > On Tue, Jul 13, 2021 at 5:49 PM Dongliang Mu wrote: > > > > On Tue, Jul 13, 2021 at 4:48 PM Sean Young wrote: > > > > > > On Wed, Jul 07, 2021 at 05:34:09PM +0800, Dongliang Mu wrote: > > > > If em28xx_ir_init fails, it would decrease the refcount of dev. However, > > > > in the em28xx_ir_fini, when ir is NULL, it goes to ref_put and decrease > > > > the refcount of dev. This will lead to a refcount bug. > > > > > > > > Fix this bug by removing the kref_put in the error handling code > > > > of em28xx_ir_init. > > > > > > > > refcount_t: underflow; use-after-free. > > > > WARNING: CPU: 0 PID: 7 at lib/refcount.c:28 refcount_warn_saturate+0x18e/0x1a0 lib/refcount.c:28 > > > > Modules linked in: > > > > CPU: 0 PID: 7 Comm: kworker/0:1 Not tainted 5.13.0 #3 > > > > Workqueue: usb_hub_wq hub_event > > > > RIP: 0010:refcount_warn_saturate+0x18e/0x1a0 lib/refcount.c:28 > > > > Call Trace: > > > > kref_put.constprop.0+0x60/0x85 include/linux/kref.h:69 > > > > em28xx_usb_disconnect.cold+0xd7/0xdc drivers/media/usb/em28xx/em28xx-cards.c:4150 > > > > usb_unbind_interface+0xbf/0x3a0 drivers/usb/core/driver.c:458 > > > > __device_release_driver drivers/base/dd.c:1201 [inline] > > > > device_release_driver_internal+0x22a/0x230 drivers/base/dd.c:1232 > > > > bus_remove_device+0x108/0x160 drivers/base/bus.c:529 > > > > device_del+0x1fe/0x510 drivers/base/core.c:3540 > > > > usb_disable_device+0xd1/0x1d0 drivers/usb/core/message.c:1419 > > > > usb_disconnect+0x109/0x330 drivers/usb/core/hub.c:2221 > > > > hub_port_connect drivers/usb/core/hub.c:5151 [inline] > > > > hub_port_connect_change drivers/usb/core/hub.c:5440 [inline] > > > > port_event drivers/usb/core/hub.c:5586 [inline] > > > > hub_event+0xf81/0x1d40 drivers/usb/core/hub.c:5668 > > > > process_one_work+0x2c9/0x610 kernel/workqueue.c:2276 > > > > process_scheduled_works kernel/workqueue.c:2338 [inline] > > > > worker_thread+0x333/0x5b0 kernel/workqueue.c:2424 > > > > kthread+0x188/0x1d0 kernel/kthread.c:319 > > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > > > > > > > Reported-by: Dongliang Mu > > > > Fixes: ac5688637144 ("media: em28xx: Fix possible memory leak of em28xx struct") > > > > Signed-off-by: Dongliang Mu > > > > --- > > > > v1->v2: move kref_get to the original position > > > > drivers/media/usb/em28xx/em28xx-input.c | 1 - > > > > 1 file changed, 1 deletion(-) > > > > > > > > diff --git a/drivers/media/usb/em28xx/em28xx-input.c b/drivers/media/usb/em28xx/em28xx-input.c > > > > index 59529cbf9cd0..0b6d77c3bec8 100644 > > > > --- a/drivers/media/usb/em28xx/em28xx-input.c > > > > +++ b/drivers/media/usb/em28xx/em28xx-input.c > > > > @@ -842,7 +842,6 @@ static int em28xx_ir_init(struct em28xx *dev) > > > > kfree(ir); > > > > ref_put: > > > > em28xx_shutdown_buttons(dev); > > > > - kref_put(&dev->ref, em28xx_free_device); > > > > return err; > > > > } > > > > > > Ideally we want an init function to not have any side effects if it returns > > > an error (or to do undo those side effects). With this change, the as long > > > as is_audio_only is not set, we always do a kref_get(), even in the error > > > case. As long as is_audio_only is not set, fini always does a kref_put(). > > > > > > Now this works but it's not really very readable code, and it requires that > > > the fini is called even if init returns an error. > > > > > > If an init function returns an error, it should undo any side effects like > > > allocations or reference counts. So the best way to handle this to only > > > do a kref_get() in the happy path of em28xx_ir_init(). > > > > Hi Sean, > > > > In the v1 version, I moved kref_get from the beginning to the ending. > > Do you mean this change? > > > > @@ -708,7 +708,6 @@ static int em28xx_ir_init(struct em28xx *dev) > > return 0; > > } > > > > - kref_get(&dev->ref); > > INIT_DELAYED_WORK(&dev->buttons_query_work, em28xx_query_buttons); > > > > if (dev->board.buttons) > > @@ -833,6 +832,9 @@ static int em28xx_ir_init(struct em28xx *dev) > > > > dev_info(&dev->intf->dev, "Input extension successfully initialized\n"); > > > > + /* Only increase refcount when this function is executed successfully */ > > + kref_get(&dev->ref); > > + > > return 0; > > > > Another reason not to move kref_get is that Paval comments on my patch: > > > > > kref_get() should be before this call to not trigger UAF in em28xx_query_buttons() > > > > So I think it's safe to call kref_get at the beginning. > > > > > > > > > > > Thanks > > > > > > Sean