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

[Jarkko Sakkinen]

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@xxxxxxxxxxxxxxx # v5.13+
Fixes: f2219745250f ("security: keys: trusted: use ASN.1 TPM2 key format for the blobs")
Reported-by: co+6a581c4284f721d4@xxxxxxx
Closes: https://bugs.sh/b/6a581c4284f721d4/
Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---
 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,
 		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