linux-kernel - Re: [PATCH] tpm: fix buffer overflow in /dev/tpm0

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Date:   Mon, 12 Sep 2016 10:50:57 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        "moderated list:TPM DEVICE DRIVER" 
        <tpmdd-devel@...ts.sourceforge.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: fix buffer overflow in /dev/tpm0

On Sun, Sep 11, 2016 at 10:05:46PM -0600, Jason Gunthorpe wrote:
> On Sun, Sep 11, 2016 at 03:19:00PM +0300, Jarkko Sakkinen wrote:
> > tpm_write() does not check whether the buffer has at least enough space
> > for the header before passing it to tpm_transmit() so an overflow can
> > happen.
> 
> Eh?
> 
> tpm_write uses a hard wired buffer size of TPM_BUFSIZE when working
> with tpm_transmit.
> 
> in_size is never used except for the copy. We should probably fix that
> to sanity check the header length vs in_size.
> 
> That doesn't seem to be a security issue however because the header
> length is propery limited to TPM_BUFSIZE and the data buffer is
> allocated specifically for that process using kzalloc.

I was working on something else when I bumped into this. The commit
message is not the best possible but still the issue is valid although
it does not cause any imaginable harm because there is always
TPM_BUFSIZE of room in the buffer passed by tpm_write.

I'll update the commit message not to speak about tpm_write.

"tpm_transmit() does not check whether the bufsiz can contain the TPM
header. Add check for this and return -EINVAL if it the buffer is too
small."

The check should be in tpm_transmit() and also the commit message should
be only about that.

> Jason

/Jarkko