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Date: Tue, 18 Jan 2022 10:35:33 -0800 From: Kees Cook <keescook@...omium.org> To: Stefan Berger <stefanb@...ux.ibm.com> Cc: Peter Huewe <peterhuewe@....de>, Jarkko Sakkinen <jarkko@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>, linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] tpm: vtpm_proxy: Avoid device-originated buffer overflow On Thu, Jan 13, 2022 at 04:19:32PM -0500, Stefan Berger wrote: > I just want to clarify this. In vtpm_proxy_tpm_op_send() we have the only > place that sets req_len to a value larger than 0: > > static int vtpm_proxy_tpm_op_send(struct tpm_chip *chip, u8 *buf, size_t > count) > { > struct proxy_dev *proxy_dev = dev_get_drvdata(&chip->dev); > > if (count > sizeof(proxy_dev->buffer)) { > dev_err(&chip->dev, > "Invalid size in send: count=%zd, buffer size=%zd\n", > count, sizeof(proxy_dev->buffer)); > return -EIO; > } > > [...] > > proxy_dev->req_len = count; > memcpy(proxy_dev->buffer, buf, count); > > [...] > > } > > > The above makes sure that we cannot copy more bytes into the > proxy_dev->buffer than the what the buffer has bytes for. > > It then sets req_len to a valid value that is less or equal to the buffer > size. > > Considering this your check above seems to only be there to make the > compiler happy but otherwise I don't see that this is a real problem with a > buffer overflow?! > > Nevertheless, let all those compilers be happy: > > Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com> Ah yes, thanks! I'll reword the commit log for v2. :) -- Kees Cook
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