[PATCH] tpm: add buffer access validation in tpm2_get_pcr_allocation()

[Nayna Jain <nayna@linux.vnet.ibm.com>]

This patch add validation in tpm2_get_pcr_allocation to avoid
access beyond response buffer length.

Suggested-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
---
 drivers/char/tpm/tpm2-cmd.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 4aad84c..02c1ea7 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -1008,9 +1008,13 @@ static ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
 	struct tpm2_pcr_selection pcr_selection;
 	struct tpm_buf buf;
 	void *marker;
-	unsigned int count = 0;
+	void *end;
+	void *pcr_select_offset;
+	unsigned int count;
+	u32 sizeof_pcr_selection;
+	u32 resp_len;
 	int rc;
-	int i;
+	int i = 0;
 
 	rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_GET_CAPABILITY);
 	if (rc)
@@ -1034,15 +1038,29 @@ static ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
 	}
 
 	marker = &buf.data[TPM_HEADER_SIZE + 9];
+
+	resp_len = be32_to_cpup((__be32 *)&buf.data[2]);
+	end = &buf.data[resp_len];
+
 	for (i = 0; i < count; i++) {
+		pcr_select_offset = marker +
+			offsetof(struct tpm2_pcr_selection, size_of_select);
+		if (pcr_select_offset >= end) {
+			rc = -EFAULT;
+			break;
+		}
+
 		memcpy(&pcr_selection, marker, sizeof(pcr_selection));
 		chip->active_banks[i] = be16_to_cpu(pcr_selection.hash_alg);
-		marker = marker + sizeof(struct tpm2_pcr_selection);
+		sizeof_pcr_selection = sizeof(pcr_selection.hash_alg) +
+			sizeof(pcr_selection.size_of_select) +
+			sizeof(u8) * pcr_selection.size_of_select;
+		marker = marker + sizeof_pcr_selection;
 	}
 
 out:
-	if (count < ARRAY_SIZE(chip->active_banks))
-		chip->active_banks[count] = TPM2_ALG_ERROR;
+	if (i < ARRAY_SIZE(chip->active_banks))
+		chip->active_banks[i] = TPM2_ALG_ERROR;
 
 	tpm_buf_destroy(&buf);
 
-- 
2.5.0