Messages in this thread Patch in this message | | | Date | Mon, 1 Apr 2019 11:32:11 -0700 | From | Kees Cook <> | Subject | [PATCH] tpm: Actually fail on TPM errors during "get random" |
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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 an 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: 7aee9c52d7ac ("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> --- drivers/char/tpm/tpm1-cmd.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c index 85dcf2654d11..faeb78ecf960 100644 --- a/drivers/char/tpm/tpm1-cmd.c +++ 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) { @@ -524,7 +524,7 @@ int tpm1_get_random(struct tpm_chip *chip, u8 *dest, size_t max) rc = tpm_buf_init(&buf, TPM_TAG_RQU_COMMAND, TPM_ORD_GET_RANDOM); if (rc) - return rc; + goto fail; do { tpm_buf_append_u32(&buf, num_bytes); @@ -559,7 +559,10 @@ int tpm1_get_random(struct tpm_chip *chip, u8 *dest, size_t max) rc = total ? (int)total : -EIO; out: tpm_buf_destroy(&buf); - return rc; +fail: + if (rc < 0) + return rc; + return -EIO; } #define TPM_ORD_PCRREAD 21 -- 2.17.1
-- Kees Cook
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