Re: [PATCH v3 2/4] tpm2-sessions: Fix tpm2_read_public range checks

[Jonathan McDowell <noodles@earth.li>]

On Thu, Dec 04, 2025 at 12:12:12AM +0200, Jarkko Sakkinen wrote:
>'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>

A minor nit about variable naming, but:

Reviewed-by: Jonathan McDowell <noodles@meta.com>

>v2:
>- Made the fix localized instead of spread all over the place.
>---
> 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 be4a9c7f2e1a..34e3599f094f 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 a265e9752a5e..e9f439be3916 100644
>--- a/drivers/char/tpm/tpm2-sessions.c
>+++ b/drivers/char/tpm/tpm2-sessions.c
>@@ -163,54 +163,59 @@ static int name_size(const u8 *name)
> 	}
> }
>
>-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]);

rc2 is not great naming. We only use it for this, so perhaps name_len?

>+
>+	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
>

J.

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