Commit 782779b6 authored Apr 01, 2019 by Kees Cook Committed by Jarkko Sakkinen Jun 24, 2019

tpm: Actually fail on TPM errors during "get random"

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 <baker1tex@gmail.com>
Reported-by: Craig Robson <craig@zhatt.com>
Fixes: 7aee9c52 ("tpm: tpm1: rewrite tpm1_get_random() using tpm_buf structure")
Cc: Laura Abbott <labbott@redhat.com>
Cc: Tomas Winkler <tomas.winkler@intel.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Tomas Winkler <tomas.winkler@intel.com>
Tested-by: Bartosz Szczepanek <bsz@semihalf.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

parent c88e40e0

drivers/char/tpm/tpm1-cmd.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -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];

drivers/char/tpm/tpm2-cmd.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -297,7 +297,7 @@ struct tpm2_get_random_out {
		*
		* Return:
		* size of the buffer on success,
		* -errno otherwise
		* -errno otherwise (positive TPM return codes are masked to -EIO)
		*/
		int tpm2_get_random(struct tpm_chip chip, u8 dest, size_t max)
		{
		@@ -324,8 +324,11 @@ int tpm2_get_random(struct tpm_chip chip, u8 dest, size_t max)
		offsetof(struct tpm2_get_random_out,
		buffer),
		"attempting get random");
		if (err)
		if (err) {
		if (err > 0)
		err = -EIO;
		goto out;
		}

		out = (struct tpm2_get_random_out *)
		&buf.data[TPM_HEADER_SIZE];