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@xxxxxxxxx> Reported-by: Craig Robson <craig@xxxxxxxxx> Fixes: 7aee9c52d7ac ("tpm: tpm1: rewrite tpm1_get_random() using tpm_buf structure") Cc: Laura Abbott <labbott@xxxxxxxxxx> Cc: Tomas Winkler <tomas.winkler@xxxxxxxxx> Cc: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- 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 --- 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) { @@ -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 --- a/drivers/char/tpm/tpm2-cmd.c +++ 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) */ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max) { @@ -328,8 +328,11 @@ 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]; -- 2.17.1 -- Kees Cook
