Messages in this thread | | | Subject | Re: [PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip | From | Stefan Berger <> | Date | Thu, 4 Feb 2021 20:44:48 -0500 |
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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@kunbus.com> >> >> 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@kunbus.com> > > Tested-by: Stefan Berger <stefanb@linux.ibm.com> > > 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
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