linux-kernel - Re: [PATCH] tpm: Fix NULL pointer dereference in tpm

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Date:   Thu, 5 Jul 2018 09:29:34 +0530
From:   "S, Shirish" <sshankar@....com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Shirish S <shirish.s@....com>
Cc:     linux-integrity@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: Fix NULL pointer dereference in tpm_transmit()



On 7/4/2018 10:43 PM, Jarkko Sakkinen wrote:
> On Wed, Jul 04, 2018 at 02:33:40PM +0530, Shirish S wrote:
>> During system shutdown,
>> tpm_class_shutdown() when called with TPM_CHIP_FLAG_TPM2
>> flag set, makes chip->ops NULL.
>>
>> However tpm_chip_unregister() called later in shutdown
>> sequence tries to access chip->ops in tpm_try_transmit()
>> leading the NULL pointer dereference.
>>
>> This patch fixes this issue.
>> Below is the trace for reference:
>>
>> BUG: unable to handle kernel NULL pointer dereference at
>> 0000000000000048
>> IP: tpm_transmit+0x267/0x565
>> PGD 0 P4D 0
>> Oops: 0000 [#1] PREEMPT SMP NOPTI
>> ...
>> task: ffff937c847fe580 task.stack: ffffa79f80b04000
>> RIP: 0010:tpm_transmit+0x267/0x565
>> RSP: 0018:ffffa79f80b07c08 EFLAGS: 00010286
>> RAX: 0000000000000000 RBX: ffff937ca9bc8000 RCX: ffff937c847fe580
>> RDX: 0000000000000000 RSI: 0000000000000002 RDI: ffffffff98e3cd40
>> RBP: ffffa79f80b07c88 R08: 000000000001fff4 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000000 R12: ffffa79f80b07cd4
>> R13: 000000000000008c R14: ffffffffffffffc3 R15: 0000000000000000
>> FS:  00007ef31f747740(0000) GS:ffff937caed00000(0000)
>> knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000000000000048 CR3: 00000001243d2000 CR4: 00000000001406e0
>> Call Trace:
>> tpm_transmit_cmd+0x25/0x70
>> tpm2_shutdown+0x69/0xa3
>> ? __radix_tree_replace+0xd9/0x120
>> ? idr_replace_ext+0x92/0xb6
>> tpm_chip_unregister+0xaa/0xdb
>> cr50_i2c_shutdown+0x1e/0x41
>> device_shutdown+0x157/0x193
>> kernel_power_off+0x35/0x6e
>> SYSC_reboot+0x120/0x1a3
>> ? do_writepages+0x36/0x6e
>> ? do_writepages+0x36/0x6e
>> ? sync_inodes_one_sb+0x17/0x17
>> ? _raw_spin_unlock+0xe/0x20
>> ? iput+0x87/0x1bd
>> do_syscall_64+0x64/0x72
>> entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>>
>> Signed-off-by: Shirish S <shirish.s@....com>
>> ---
>>   drivers/char/tpm/tpm-interface.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>> index e32f6e8..b14d196 100644
>> --- a/drivers/char/tpm/tpm-interface.c
>> +++ b/drivers/char/tpm/tpm-interface.c
>> @@ -411,6 +411,14 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip,
>>   	unsigned long stop;
>>   	bool need_locality;
>>   
>> +	/* chip->ops is made NULL in tpm_class_shutdown()
>> +	 * This case is hit when tpm_chip_unregister() is called post
>> +	 * tpm_class_shutdown(), hence exit early and return
>> +	 * transmit operation not permitted
>> +	 */
>> +	if (!chip->ops)
>> +		return -EPERM;
>> +
>>   	rc = tpm_validate_command(chip, space, buf, bufsiz);
>>   	if (rc == -EINVAL)
>>   		return rc;
>> -- 
>> 2.7.4
>>
> What is cr50 anyway?
Please ignore this patch, i realised the cr50 is not yet upstreamed.
Hence the issue lies in in cr50 and not tpm driver.
Thanks.
Regards,
Shirish S
> /Jarkko

-- 
Regards,
Shirish S