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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 6C0A4C433DB for ; Wed, 3 Feb 2021 01:09:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CB3C64F5F for ; Wed, 3 Feb 2021 01:09:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229572AbhBCBJv (ORCPT ); Tue, 2 Feb 2021 20:09:51 -0500 Received: from mail.kernel.org ([198.145.29.99]:34194 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229570AbhBCBJu (ORCPT ); Tue, 2 Feb 2021 20:09:50 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id F09F664F59; Wed, 3 Feb 2021 01:09:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612314548; bh=HOgKBBbXaavpK1QmCgpeqtlhU/D1f5hiJDLNDTcIzno=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OM7nlRPP39RoXe0gXaU2XzqknPFJqkgGsOls6H2PXiS0QesK/SSN+tSRSGPp/bTV7 A4REv8iO0RHBvVJ76zmq1/t6PE/xTYOAJepSjn7DjjIgB4E/NgcqQY1yPcUyZxCWVE g2bOnk7osRGkV0sY8Iu9c0r5jQAYdQhmvGNrHZCyIPfxNFLD+Im6Z6UmlDeEYx3cCL iKAhAXqsjovxlOE1YpHUix8iBQs/j4UL3QiE1BD6ZFbfyD60F3b+pXXlmBAiMTzVGF QxZ/hPuAIjAOHTz/gF8FP/35ShGRvEx0Hg+wZXypCLqzF0D/1YhiXG6ROO+DlCfHx3 ufOzfr69A3yfA== Date: Wed, 3 Feb 2021 03:09:01 +0200 From: Jarkko Sakkinen To: Lino Sanfilippo Cc: peterhuewe@gmx.de, jgg@ziepe.ca, stefanb@linux.vnet.ibm.com, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, Lino Sanfilippo , James.Bottomley@hansenpartnership.com Subject: Re: [PATCH v2 1/3] tpm: fix reference counting for struct tpm_chip Message-ID: References: <1612303743-29017-1-git-send-email-LinoSanfilippo@gmx.de> <1612303743-29017-2-git-send-email-LinoSanfilippo@gmx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1612303743-29017-2-git-send-email-LinoSanfilippo@gmx.de> Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Tue, Feb 02, 2021 at 11:09:01PM +0100, Lino Sanfilippo wrote: > From: Lino Sanfilippo > > The following sequence of operations > > 1. open device /dev/tpmrm > 2. remove the registered tpm chip driver What is "tpm chip driver"? Please just refer to the exact thing (e.g. tpm_tis_spi is the one you should refer to in your case). > 3. perform a write() to /dev/tpmrm Just a nit: Use capital letter as the first letter in sentences. If I do "rmmod tpm_tis" the device is gone. > results in a refcount warning: > > ------------[ cut here ]------------ > WARNING: CPU: 3 PID: 1161 at lib/refcount.c:25 kobject_get+0xa0/0xa4 > refcount_t: addition on 0; use-after-free. > Modules linked in: tpm_tis_spi tpm_tis_core tpm mdio_bcm_unimac brcmfmac > sha256_generic libsha256 sha256_arm hci_uart btbcm bluetooth cfg80211 vc4 > brcmutil ecdh_generic ecc snd_soc_core crc32_arm_ce libaes > raspberrypi_hwmon ac97_bus snd_pcm_dmaengine bcm2711_thermal snd_pcm > snd_timer genet snd phy_generic soundcore [last unloaded: spi_bcm2835] > CPU: 3 PID: 1161 Comm: hold_open Not tainted 5.10.0ls-main-dirty #2 > Hardware name: BCM2711 > [] (unwind_backtrace) from [] (show_stack+0x10/0x14) > [] (show_stack) from [] (dump_stack+0xc4/0xd8) > [] (dump_stack) from [] (__warn+0x104/0x108) > [] (__warn) from [] (warn_slowpath_fmt+0x74/0xb8) > [] (warn_slowpath_fmt) from [] (kobject_get+0xa0/0xa4) > [] (kobject_get) from [] (tpm_try_get_ops+0x14/0x54 [tpm]) > [] (tpm_try_get_ops [tpm]) from [] (tpm_common_write+0x38/0x60 [tpm]) > [] (tpm_common_write [tpm]) from [] (vfs_write+0xc4/0x3c0) > [] (vfs_write) from [] (ksys_write+0x58/0xcc) > [] (ksys_write) from [] (ret_fast_syscall+0x0/0x4c) > Exception stack(0xc226bfa8 to 0xc226bff0) > bfa0: 00000000 000105b4 00000003 beafe664 00000014 00000000 > bfc0: 00000000 000105b4 000103f8 00000004 00000000 00000000 b6f9c000 beafe684 > bfe0: 0000006c beafe648 0001056c b6eb6944 > ---[ end trace d4b8409def9b8b1f ]--- I guess this is happening with tpm_tis_spi. Unfortunately I don't have anything available that would use it. I did testing with tpm_tis but so far no success reproducing. > > The reason is an attempt to get the chip->dev reference (see > tpm_try_get_ops()) although the last reference to this device has already > been released with the unregistration of the chip driver. > > As far as I understand, the history of this bug is as follows: Generally you don't write in person to a commit message. This not an email in that sense. You should write in imperative form. > Commit fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm") > introduced the support for /dev/tpmrm. Beside the new device chip->devs > this code introduced the taking of an extra reference to chip->dev to > ensure that this device is not released as long as /dev/tpmrm is still in > use: > > + chip->devs.release = tpm_devs_release; > + /* get extra reference on main device to hold on > + * behalf of devs. This holds the chip structure > + * while cdevs is in use. The corresponding put > + * is in the tpm_devs_release > + */ Copy pasting this is probably unnecessary. > The extra reference to chip->dev was supposed to be released as soon as the > reference to chip->devs was freed: > > +static void tpm_devs_release(struct device *dev) > +{ > + struct tpm_chip *chip = container_of(dev, struct tpm_chip, devs); > + > + /* release the master device reference */ > + put_device(&chip->dev); > +} OK, what you really should explain in the commit message is: 1. Why this function *is not* called. 2. What your fix does to make things better. > However the code did not work as expected, because the reference to > chip->devs was never released. Thus tpm_devs_release() was never called > which in turn also prevented the extra reference to chip->dev from being > released. If it did not work, it works now :-) So any fix would not be required. Just making a point here. > This led to behaviour which commit 8979b02aaf1d ("tpm: Fix reference count > to main device") tried to fix as an excerpt of the commit message shows: > > "The main device is currently not properly released due to one additional > reference to the 'devs' device which is only released in case of a TPM 2. > So, also get the additional reference only in case of a TPM2." > > Instead of adding the missing put for chip->devs, this patch chose another > approach by only taking the reference in case of TPM2: > > + if (chip->flags & TPM_CHIP_FLAG_TPM2) > + get_device(&chip->dev); > > This fixed the non-TPM2 case but left the TPM2 case without the required > extra reference, since there is no code path that ever sets the flag > TPM_CHIP_FLAG_TPM2, which is the situation we have todoay. You should not need this explanation to explain refcount mismatch. Also past tense should not be used. I appreciate the time taken to write all this but you should just explain what you do and why. Let's just say this explanation is very obfuscted and hard to follow. > To fix this > > 1. revert commit 8979b02aaf1d ("tpm: Fix reference count to main device") > to make sure the extra reference is taken unconditionally as proposed by > commit fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm") > 2. fix commit fdc915f7f719 ("tpm: expose spaces via a device link > > /dev/tpmrm") by adding an action handler to do the missing put to > chip->devs. This eventually results in the call of function > tpm_devs_release() which in turn performs the final put to the extra > reference to chip->dev. > > Fixes: fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm") > Fixes: 8979b02aaf1d ("tpm: Fix reference count to main device") If the fix makes sense a Cc stable is also required. > Signed-off-by: Lino Sanfilippo > --- > drivers/char/tpm/tpm-chip.c | 18 +++++++++++++++--- > drivers/char/tpm/tpm_ftpm_tee.c | 2 ++ > drivers/char/tpm/tpm_vtpm_proxy.c | 1 + > 3 files changed, 18 insertions(+), 3 deletions(-) > > diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c > index ddaeceb..3ace199 100644 > --- a/drivers/char/tpm/tpm-chip.c > +++ b/drivers/char/tpm/tpm-chip.c > @@ -360,8 +360,7 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev, > * while cdevs is in use. The corresponding put > * is in the tpm_devs_release (TPM2 only) > */ > - if (chip->flags & TPM_CHIP_FLAG_TPM2) > - get_device(&chip->dev); > + get_device(&chip->dev); > > if (chip->dev_num == 0) > chip->dev.devt = MKDEV(MISC_MAJOR, TPM_MINOR); > @@ -422,8 +421,21 @@ struct tpm_chip *tpmm_chip_alloc(struct device *pdev, > rc = devm_add_action_or_reset(pdev, > (void (*)(void *)) put_device, > &chip->dev); > - if (rc) > + if (rc) { > + put_device(&chip->devs); > return ERR_PTR(rc); > + } > + > + rc = devm_add_action_or_reset(pdev, > + (void (*)(void *)) put_device, > + &chip->devs); > + if (rc) { > + devm_remove_action(pdev, > + (void (*)(void *)) put_device, > + &chip->dev); > + put_device(&chip->dev); > + return ERR_PTR(rc); > + } > > dev_set_drvdata(pdev, chip); > > diff --git a/drivers/char/tpm/tpm_ftpm_tee.c b/drivers/char/tpm/tpm_ftpm_tee.c > index 2ccdf8a..82858c2 100644 > --- a/drivers/char/tpm/tpm_ftpm_tee.c > +++ b/drivers/char/tpm/tpm_ftpm_tee.c > @@ -286,6 +286,7 @@ static int ftpm_tee_probe(struct device *dev) > > out_chip: > put_device(&pvt_data->chip->dev); > + put_device(&pvt_data->chip->devs); > out_chip_alloc: > tee_shm_free(pvt_data->shm); > out_shm_alloc: > @@ -318,6 +319,7 @@ static int ftpm_tee_remove(struct device *dev) > tpm_chip_unregister(pvt_data->chip); > > /* frees chip */ > + put_device(&pvt_data->chip->devs); > put_device(&pvt_data->chip->dev); > > /* Free the shared memory pool */ > diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c > index 91c772e3..97b60f8 100644 > --- a/drivers/char/tpm/tpm_vtpm_proxy.c > +++ b/drivers/char/tpm/tpm_vtpm_proxy.c > @@ -520,6 +520,7 @@ static struct proxy_dev *vtpm_proxy_create_proxy_dev(void) > */ > static inline void vtpm_proxy_delete_proxy_dev(struct proxy_dev *proxy_dev) > { > + put_device(&proxy_dev->chip->devs); > put_device(&proxy_dev->chip->dev); /* frees chip */ > kfree(proxy_dev); > } > -- > 2.7.4 > Hope this feedback helps to improve. You really need to rewrite the whole commit message. I wonder who could try to reproduce this. With a quick skim I get the issue. Also you don't have James Bottomley in the CC list of the patch who is the author of the original commit. Please sort that out too... /Jarkko