Re: [PATCH] KEYS: trusted: Fix tpm2_load_cmd() boundary check

[Stefano Garzarella <sgarzare@redhat.com>]

On Tue, Sep 01, 2026 at 11:58:06PM +0300, Jarkko Sakkinen wrote:
>tpm2_load_cmd() does boundary checks against the ASN.1 size i.e.,
>payload->blob_len. Address this by passing the decoded blob size to
>tpm2_load_cmd(), and use it for the boundary checks.
>
>Cc: stable@vger.kernel.org # v5.13+
>Fixes: f2219745250f ("security: keys: trusted: use ASN.1 TPM2 key format for the blobs")
>Reported-by: co+6a581c4284f721d4@bugs.sh
>Closes: https://bugs.sh/b/6a581c4284f721d4/
>Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
>---
> security/keys/trusted-keys/trusted_tpm2.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
>diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
>index 67225dd562a9..01f18bb37047 100644
>--- a/security/keys/trusted-keys/trusted_tpm2.c
>+++ b/security/keys/trusted-keys/trusted_tpm2.c
>@@ -99,7 +99,7 @@ struct tpm2_key_context {
>
> static int tpm2_key_decode(struct trusted_key_payload *payload,
> 			   struct trusted_key_options *options,
>-			   u8 **buf)
>+			   u8 **buf, unsigned int *blob_len)
> {
> 	int ret;
> 	struct tpm2_key_context ctx;
>@@ -120,6 +120,7 @@ static int tpm2_key_decode(struct trusted_key_payload *payload,

	blob = kmalloc(ctx.priv_len + ctx.pub_len + 4, GFP_KERNEL);

Pre-existing, but is `+ 4` here useless?

I'm not asking to fix here, just noticed while reviewing.
Maybe we can set *blob_len earlier and use it also in the kmalloc().
Not a strong opinion, that said this LGTM:

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

	if (!blob)
> 		return -ENOMEM;
>
> 	*buf = blob;
>+	*blob_len = ctx.priv_len + ctx.pub_len;
> 	options->keyhandle = ctx.parent;
>
> 	memcpy(blob, ctx.priv, ctx.priv_len);
>@@ -384,10 +385,11 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
> 	int rc;
> 	u32 attrs;
>
>-	rc = tpm2_key_decode(payload, options, &blob);
>+	rc = tpm2_key_decode(payload, options, &blob, &blob_len);
> 	if (rc) {
> 		/* old form */
> 		blob = payload->blob;
>+		blob_len = payload->blob_len;
> 		payload->old_format = 1;
> 	} else {
> 		/* Bind for cleanup: */
>@@ -399,17 +401,17 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
> 		return -EINVAL;
>
> 	/* must be big enough for at least the two be16 size counts */
>-	if (payload->blob_len < 4)
>+	if (blob_len < 4)
> 		return -EINVAL;
>
> 	private_len = get_unaligned_be16(blob);
>
> 	/* must be big enough for following public_len */
>-	if (private_len + 2 + 2 > (payload->blob_len))
>+	if (private_len + 2 + 2 > blob_len)
> 		return -E2BIG;
>
> 	public_len = get_unaligned_be16(blob + 2 + private_len);
>-	if (private_len + 2 + public_len + 2 > payload->blob_len)
>+	if (private_len + 2 + public_len + 2 > blob_len)
> 		return -E2BIG;
>
> 	pub = blob + 2 + private_len + 2;
>-- 
>2.47.3
>