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 <[email protected]> Reported-by: Craig Robson <[email protected]> Fixes: 7aee9c52d7ac ("tpm: tpm1: rewrite tpm1_get_random() using tpm_buf structure") Cc: Laura Abbott <[email protected]> Cc: Tomas Winkler <[email protected]> Cc: Jarkko Sakkinen <[email protected]> Cc: [email protected] Signed-off-by: Kees Cook <[email protected]> --- 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
