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[156.34.49.251]) by smtp.gmail.com with ESMTPSA id u16sm5765641qkj.50.2019.04.01.12.09.55 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 01 Apr 2019 12:09:56 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hB2Jf-0006fZ-2N; Mon, 01 Apr 2019 16:09:55 -0300 Date: Mon, 1 Apr 2019 16:09:55 -0300 From: Jason Gunthorpe To: Kees Cook Cc: Jarkko Sakkinen , James Bottomley , Phil Baker , Craig Robson , Laura Abbott , Tomas Winkler , linux-kernel@vger.kernel.org, Peter Huewe , Arnd Bergmann , linux-integrity@vger.kernel.org Subject: Re: [PATCH v3] tpm: Actually fail on TPM errors during "get random" Message-ID: <20190401190955.GJ6209@ziepe.ca> References: <20190401190607.GA23795@beast> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190401190607.GA23795@beast> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 01, 2019 at 12:06:07PM -0700, Kees Cook wrote: > A "get random" may fail with a TPM error, but those codes were returned > as-is to the caller, which assumed the result was the number of bytes > that had been written to the target buffer, which could lead to a kernel > heap memory exposure and over-read. > > This fixes tpm1_get_random() to mask positive TPM errors into -EIO, as > before. > > [ 18.092103] tpm tpm0: A TPM error (379) occurred attempting get random > [ 18.092106] usercopy: Kernel memory exposure attempt detected from SLUB object 'kmalloc-64' (offset 0, size 379)! > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1650989 > Reported-by: Phil Baker > Reported-by: Craig Robson > Fixes: 7aee9c52d7ac ("tpm: tpm1: rewrite tpm1_get_random() using tpm_buf structure") > Cc: Laura Abbott > Cc: Tomas Winkler > Cc: Jarkko Sakkinen > Cc: stable@vger.kernel.org > Signed-off-by: Kees Cook > v3: fix never-succeed, limit checks to tpm cmd return (James, Jason) > v2: also fix tpm2 implementation (Jason Gunthorpe) > drivers/char/tpm/tpm1-cmd.c | 7 +++++-- > drivers/char/tpm/tpm2-cmd.c | 7 +++++-- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c > index 85dcf2654d11..faacbe1ffa1a 100644 > +++ b/drivers/char/tpm/tpm1-cmd.c > @@ -510,7 +510,7 @@ struct tpm1_get_random_out { > * > * Return: > * * number of bytes read > - * * -errno or a TPM return code otherwise > + * * -errno (positive TPM return codes are masked to -EIO) > */ > int tpm1_get_random(struct tpm_chip *chip, u8 *dest, size_t max) > { > @@ -531,8 +531,11 @@ int tpm1_get_random(struct tpm_chip *chip, u8 *dest, size_t max) > > rc = tpm_transmit_cmd(chip, &buf, sizeof(out->rng_data_len), > "attempting get random"); > - if (rc) > + if (rc) { > + if (rc > 0) > + rc = -EIO; > goto out; > + } > > out = (struct tpm1_get_random_out *)&buf.data[TPM_HEADER_SIZE]; > > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c > index e74c5b7b64bf..8ffa6af61580 100644 > +++ b/drivers/char/tpm/tpm2-cmd.c > @@ -301,7 +301,7 @@ struct tpm2_get_random_out { > * > * Return: > * size of the buffer on success, > - * -errno otherwise > + * -errno otherwise ((positive TPM return codes are masked to -EIO) Extra bracket, but otherwise looks fine to me Jason