In the Linux kernel, the following vulnerability has been resolved:
tpm: fix reference counting for struct tpm_chip
The following sequence of operations results in a refcount warning:
- Open device /dev/tpmrm.
- Remove module tpm_tis_spi.
- 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
[] (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 ]---
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")
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.
References
In the Linux kernel, the following vulnerability has been resolved:
tpm: fix reference counting for struct tpm_chip
The following sequence of operations 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 ]---
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")
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.
References