[PATCH v6 6/7] tpm: ensure that the output of PCR read contains the correct digest size
From: Roberto Sassu <roberto.sassu@huawei.com>
Date: 2018-12-04 08:27:39
Also in:
linux-security-module, lkml
Subsystem:
the rest, tpm device driver · Maintainers:
Linus Torvalds, Peter Huewe, Jarkko Sakkinen
This patch protects against data corruption that could happen in the bus, by checking that the digest size returned by the TPM during a PCR read matches the size of the algorithm passed to tpm2_pcr_read(). This check is performed after information about the PCR banks has been retrieved. Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> Reviewed-by: Jarkko Sakkinen <redacted> --- drivers/char/tpm/tpm2-cmd.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index a804f0b7126a..d6d29480348c 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c@@ -179,15 +179,28 @@ struct tpm2_pcr_read_out { int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx, struct tpm_digest *digest, u16 *digest_size_ptr) { + int i; int rc; struct tpm_buf buf; struct tpm2_pcr_read_out *out; u8 pcr_select[TPM2_PCR_SELECT_MIN] = {0}; u16 digest_size; + u16 expected_digest_size = 0; if (pcr_idx >= TPM2_PLATFORM_PCR) return -EINVAL; + if (!digest_size_ptr) { + for (i = 0; i < chip->nr_allocated_banks && + chip->allocated_banks[i].alg_id != digest->alg_id; i++) + ; + + if (i == chip->nr_allocated_banks) + return -EINVAL; + + expected_digest_size = chip->allocated_banks[i].digest_size; + } + rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_PCR_READ); if (rc) return rc;
@@ -207,7 +220,8 @@ int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx, out = (struct tpm2_pcr_read_out *)&buf.data[TPM_HEADER_SIZE]; digest_size = be16_to_cpu(out->digest_size); - if (digest_size > sizeof(digest->digest)) { + if (digest_size > sizeof(digest->digest) || + (!digest_size_ptr && digest_size != expected_digest_size)) { rc = -EINVAL; goto out; }
--
2.17.1