[PATCH v2 1/2] keys: trusted: tpm1: add bounds check in tpm_seal() before memcpy

[Sanket Sharma]

tpm_seal() computes storedsize from TPM response fields and passes
it directly to memcpy() into a MAX_BLOB_SIZE buffer without bounds
validation. A forged TPM response can set storedsize to 4086,
overflowing the 512-byte blob by 3574 bytes into adjacent slab
objects.

Add a check that storedsize does not exceed MAX_BLOB_SIZE before
the memcpy, returning -EINVAL on oversized responses.

Signed-off-by: Sanket Sharma <sanketsharmacsec@xxxxxxxxx>
---
 security/keys/trusted-keys/trusted_tpm1.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index 8f57c6111..d47cb7108 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -531,6 +531,10 @@ static int tpm_seal(struct tpm_buf *tb, uint16_t keytype,
 
 	/* copy the returned blob to caller */
 	if (!ret) {
+		if (storedsize > MAX_BLOB_SIZE) {
+			ret = -EINVAL;
+			goto out;
+		}
 		memcpy(blob, tb->data + TPM_DATA_OFFSET, storedsize);
 		*bloblen = storedsize;
 	}
-- 
2.53.0