Re: [PATCH v8 1/1] tpm: fix reference counting for struct tpm_chip

[Jarkko Sakkinen]

On Tue, Mar 01, 2022 at 07:36:34AM -0500, Stefan Berger wrote:
> 
> On 2/28/22 21:21, Lino Sanfilippo wrote:
> > From: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
> > 
> > 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.
> > 
> > ------------[ 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
> > [<c0410c3c>] (unwind_backtrace) from [<c040b580>] (show_stack+0x10/0x14)
> > [<c040b580>] (show_stack) from [<c1092174>] (dump_stack+0xc4/0xd8)
> > [<c1092174>] (dump_stack) from [<c0445a30>] (__warn+0x104/0x108)
> > [<c0445a30>] (__warn) from [<c0445aa8>] (warn_slowpath_fmt+0x74/0xb8)
> > [<c0445aa8>] (warn_slowpath_fmt) from [<c08435d0>] (kobject_get+0xa0/0xa4)
> > [<c08435d0>] (kobject_get) from [<bf0a715c>] (tpm_try_get_ops+0x14/0x54 [tpm])
> > [<bf0a715c>] (tpm_try_get_ops [tpm]) from [<bf0a7d6c>] (tpm_common_write+0x38/0x60 [tpm])
> > [<bf0a7d6c>] (tpm_common_write [tpm]) from [<c05a7ac0>] (vfs_write+0xc4/0x3c0)
> > [<c05a7ac0>] (vfs_write) from [<c05a7ee4>] (ksys_write+0x58/0xcc)
> > [<c05a7ee4>] (ksys_write) from [<c04001a0>] (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 ]---
> > 
> > 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 moving the TPM 2 character device handling from
> > tpm_chip_alloc() to tpm_add_char_device() which is called at a later point
> > in time when the flag has been set in case of TPM2.
> > 
> > Commit fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm<n>")
> > 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.
> > 
> > Fix this by putting chip->devs in tpm_chip_unregister().
> > 
> > Finally move the new implementation for the TPM 2 handling into a new
> > function to avoid multiple checks for the TPM_CHIP_FLAG_TPM2 flag in the
> > good case and error cases.
> > 
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm<n>")
> > Fixes: 8979b02aaf1d ("tpm: Fix reference count to main device")
> > Co-developed-by: Jason Gunthorpe <jgg@xxxxxxxx>
> > Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxx>
> > Signed-off-by: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
> 
> Tested-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>

Thanks, would be it be possible to also check v9?

BR, Jarkko