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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id e7sm7783668qtj.48.2021.02.05.05.05.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Feb 2021 05:05:12 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1l80nP-003pgK-Ip; Fri, 05 Feb 2021 09:05:11 -0400 Date: Fri, 5 Feb 2021 09:05:11 -0400 From: Jason Gunthorpe To: Lino Sanfilippo Cc: peterhuewe@gmx.de, jarkko@kernel.org, stefanb@linux.vnet.ibm.com, James.Bottomley@hansenpartnership.com, stable@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, Lino Sanfilippo Subject: Re: [PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip Message-ID: <20210205130511.GI4718@ziepe.ca> References: <1612482643-11796-1-git-send-email-LinoSanfilippo@gmx.de> <1612482643-11796-2-git-send-email-LinoSanfilippo@gmx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1612482643-11796-2-git-send-email-LinoSanfilippo@gmx.de> Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Fri, Feb 05, 2021 at 12:50:42AM +0100, Lino Sanfilippo wrote: > From: Lino Sanfilippo > > The following sequence of operations results in a refcount warning: > > 1. Open device /dev/tpmrm > 2. Remove module tpm_tis_spi > 3. Write a TPM command to the file descriptor opened at step 1. > > 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 > > The reason for this warning is the attempt to get the chip->dev reference > in tpm_common_write() although the reference counter is already zero. > Since commit 8979b02aaf1d ("tpm: Fix reference count to main device") the > extra reference used to prevent a premature zero counter is never taken, > because the required TPM_CHIP_FLAG_TPM2 flag is never set. > > Fix this by removing the flag condition. > > Commit fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm") > already introduced function tpm_devs_release() to release the extra > reference but did not implement the required put on chip->devs that results > in the call of this function. Seems wonky, the devs is just supposed to be a side thing, nothing should be using it as a primary reference count for a tpm. The bug here is only that tpm_common_open() did not get a kref on the chip before putting it in priv and linking it to the fd. See the comment before tpm_try_get_ops() indicating the caller must already have taken care to ensure the chip is valid. This should be all you need to fix the oops: diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c index 1784530b8387bb..1b738dca7fffb5 100644 --- a/drivers/char/tpm/tpm-dev-common.c +++ b/drivers/char/tpm/tpm-dev-common.c @@ -105,6 +105,7 @@ static void tpm_timeout_work(struct work_struct *work) void tpm_common_open(struct file *file, struct tpm_chip *chip, struct file_priv *priv, struct tpm_space *space) { + get_device(&priv->chip.dev); priv->chip = chip; priv->space = space; priv->response_read = true; @@ -261,6 +262,7 @@ void tpm_common_release(struct file *file, struct file_priv *priv) flush_work(&priv->timeout_work); file->private_data = NULL; priv->response_length = 0; + put_device(&chip->dev); } int __init tpm_dev_common_init(void) > Fix this also by installing an action handler that puts chip->devs as soon > as the chip is unregistered. > > Fixes: fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm") > Fixes: 8979b02aaf1d ("tpm: Fix reference count to main device") > 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 > +++ 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); This isn't right read what 'or_reset' does Jason