On 2/4/21 7:46 PM, Stefan Berger wrote:
On 2/4/21 6:50 PM, 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 removing the flag condition.
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 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<n>")
Fixes: 8979b02aaf1d ("tpm: Fix reference count to main device")
Signed-off-by: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
Tested-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Steps:
modprobe tpm_vtpm_proxy
swtpm chardev --vtpm-proxy --tpm2 --tpmstate dir=./ &
exec 100<>/dev/tpmrm1
kill -9 <swtpm pid>
rmmod tpm_vtpm_proxy
exec 100>&- # fails before, works after --> great job! :-)
To clarify: When I tested this I had *both* patches applied. Without the
patches I got the null pointer exception in tpm2_del_space(). The 2nd
patch alone solves that issue when using the steps above.
[ 525.647443] [c000000005d3bba0] [c000000000e81d78]
mutex_lock+0x28/0x90 (unreliable)
[ 525.647539] [c000000005d3bbd0] [c0080000001f5da0]
tpm2_del_space+0x48/0x130 [tpm]
[ 525.647635] [c000000005d3bc20] [c0080000001f56b8]
tpmrm_release+0x40/0x70 [tpm]
[ 525.647746] [c000000005d3bc50] [c0000000004bf718] __fput+0xb8/0x340
[ 525.647842] [c000000005d3bca0] [c00000000017def4]
task_work_run+0xe4/0x150
[ 525.647930] [c000000005d3bcf0] [c00000000001feb4]
do_notify_resume+0x484/0x4f0
[ 525.648023] [c000000005d3bdb0] [c000000000033a64]
syscall_exit_prepare+0x1d4/0x330
[ 525.648115] [c000000005d3be20] [c00000000000d96c]
system_call_common+0xfc/0x27c
