[PATCH 2/4] tpm2-sessions: Fix tpm2_read_public range checks

Jarkko Sakkinen
2025-12-01T22:46:14Z

'tpm2_read_public' has some rudimentary range checks but the function
does not ensure that the response buffer has enough bytes for the full
TPMT_HA payload.

Re-implement the function with necessary checks and validation.

Cc: stable@vger.kernel.org # v6.10+
Fixes: d0a25bb961e6 ("tpm: Add HMAC session name/handle append")
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
drivers/char/tpm/tpm2-cmd.c | 3 ++
drivers/char/tpm/tpm2-sessions.c | 77 +++++++++++++++++---------------
2 files changed, 44 insertions(+), 36 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 4473b81122e8..58a8477cda85 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -11,8 +11,11 @@
* used by the kernel internally.
*/

+#include "linux/dev_printk.h"
+#include "linux/tpm.h"
#include "tpm.h"
#include <crypto/hash_info.h>
+#include <linux/unaligned.h>

static bool disable_pcr_integrity;
module_param(disable_pcr_integrity, bool, 0444);
diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 33ad0d668e1a..afbca03f639e 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -164,54 +164,59 @@ static int name_size(const u8 *name)
return -EINVAL;
}

-static int tpm2_parse_read_public(char *name, struct tpm_buf *buf)
+static int tpm2_read_public(struct tpm_chip *chip, u32 handle, void *name)
{
- struct tpm_header *head = (struct tpm_header *)buf->data;
+ u32 mso = tpm2_handle_mso(handle);
off_t offset = TPM_HEADER_SIZE;
- u32 tot_len = be32_to_cpu(head->length);
- int ret;
- u32 val;
-
- /* we're starting after the header so adjust the length */
- tot_len -= TPM_HEADER_SIZE;
-
- /* skip public */
- val = tpm_buf_read_u16(buf, &offset);
- if (val > tot_len)
- return -EINVAL;
- offset += val;
- /* name */
-
- val = tpm_buf_read_u16(buf, &offset);
- ret = name_size(&buf->data[offset]);
- if (ret < 0)
- return ret;
+ struct tpm_buf buf;
+ int rc, rc2;

- if (val != ret)
+ if (mso != TPM2_MSO_PERSISTENT && mso != TPM2_MSO_VOLATILE &&
+ mso != TPM2_MSO_NVRAM)
return -EINVAL;

- memcpy(name, &buf->data[offset], val);
- /* forget the rest */
- return 0;
-}
-
-static int tpm2_read_public(struct tpm_chip *chip, u32 handle, char *name)
-{
- struct tpm_buf buf;
- int rc;
-
rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_READ_PUBLIC);
if (rc)
return rc;

tpm_buf_append_u32(&buf, handle);
- rc = tpm_transmit_cmd(chip, &buf, 0, "read public");
- if (rc == TPM2_RC_SUCCESS)
- rc = tpm2_parse_read_public(name, &buf);

- tpm_buf_destroy(&buf);
+ rc = tpm_transmit_cmd(chip, &buf, 0, "TPM2_ReadPublic");
+ if (rc) {
+ tpm_buf_destroy(&buf);
+ return tpm_ret_to_err(rc);
+ }

- return rc;
+ /* Skip TPMT_PUBLIC: */
+ offset += tpm_buf_read_u16(&buf, &offset);
+
+ /*
+ * Ensure space for the length field of TPM2B_NAME and hashAlg field of
+ * TPMT_HA (the extra four bytes).
+ */
+ if (offset + 4 > tpm_buf_length(&buf)) {
+ tpm_buf_destroy(&buf);
+ return -EIO;
+ }
+
+ rc = tpm_buf_read_u16(&buf, &offset);
+ rc2 = name_size(&buf.data[offset]);
+
+ if (rc2 < 0)
+ return rc2;
+
+ if (rc != rc2) {
+ tpm_buf_destroy(&buf);
+ return -EIO;
+ }
+
+ if (offset + rc > tpm_buf_length(&buf)) {
+ tpm_buf_destroy(&buf);
+ return -EIO;
+ }
+
+ memcpy(name, &buf.data[offset], rc);
+ return 0;
}
#endif /* CONFIG_TCG_TPM2_HMAC */

--
2.52.0