linux-kernel - Re: [PATCH v4] tpm: Managed allocations for tpm

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Message-ID: <aGW1JvClZ4lRaaqB@kernel.org>
Date: Thu, 3 Jul 2025 01:39:34 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: linux-kernel@...r.kernel.org, keyrings@...r.kernel.org,
	Stefan Berger <stefanb@...ux.ibm.com>,
	Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
	Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	"open list:TPM DEVICE DRIVER" <linux-integrity@...r.kernel.org>,
	"open list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v4] tpm: Managed allocations for tpm_buf instances

On Tue, Jul 01, 2025 at 10:51:55PM -0400, James Bottomley wrote:
> On Tue, 2025-07-01 at 17:51 +0300, Jarkko Sakkinen wrote:
> > Repeal and replace tpm_buf_init() and tpm_buf_init_sized() with
> > tpm_buf_alloc(), which returns a buffer of  memory with the struct
> > tpm_buf header at the beginning of the returned buffer. This leaves
> > 4090 bytes of free space for the payload.
> 
> Shouldn't this be accounted for in tpm_buf_append()? right now it will
> let us run off the end of the allocation by six bytes before it signals
> overflow because it's checking final length against PAGE_SIZE not
> PAGE_SIZE - sizeof(struct tpm_buf).  I realise this should be an
> impossible condition in production, but it's useful for debugging so we
> should be accurate about it to avoid hard to detect bugs.

Fully agree. Thanks for pointing this out!

> 
> Regards,
> 
> James
> 

BR, Jarkko