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 <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 Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> /Jarkko
