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

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Date:   Wed, 4 Jul 2018 20:13:57 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     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 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?

/Jarkko