[PATCH] greybus: cap: bound IMS/auth memcpy to ioctl size

[Suraj Theekshana <surajtheekshana1111@gmail.com>]

cap_get_ims_certificate() and cap_authenticate() derive copy
lengths from response payload sizes without checking the response
header size or destination capacity.

Reject responses smaller than their headers with -EMSGSIZE. Reject
certificate and signature data larger than their fixed ioctl buffers
with -E2BIG.

Signed-off-by: Suraj Theekshana <surajtheekshana1111@gmail.com>
---
 drivers/staging/greybus/authentication.c | 27 ++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/staging/greybus/authentication.c b/drivers/staging/greybus/authentication.c
index d8f2cd4..cbd28a3 100644
--- a/drivers/staging/greybus/authentication.c
+++ b/drivers/staging/greybus/authentication.c
@@ -128,9 +128,22 @@ static int cap_get_ims_certificate(struct gb_cap *cap, u32 class, u32 id,
 		goto done;
 	}
 
+	if (op->response->payload_size < sizeof(*response)) {
+		dev_err(cap->parent,
+			"invalid IMS certificate response size (%zu)\n",
+			op->response->payload_size);
+		ret = -EMSGSIZE;
+		goto done;
+	}
+
 	response = op->response->payload;
 	*result = response->result_code;
 	*size = op->response->payload_size - sizeof(*response);
+	if (*size > CAP_CERTIFICATE_MAX_SIZE) {
+		dev_err(cap->parent, "IMS certificate too large (%u)\n", *size);
+		ret = -E2BIG;
+		goto done;
+	}
 	memcpy(certificate, response->certificate, *size);
 
 done:
@@ -167,9 +180,23 @@ static int cap_authenticate(struct gb_cap *cap, u32 auth_type, u8 *uid,
 		goto done;
 	}
 
+	if (op->response->payload_size < sizeof(*response)) {
+		dev_err(cap->parent,
+			"invalid authenticate response size (%zu)\n",
+			op->response->payload_size);
+		ret = -EMSGSIZE;
+		goto done;
+	}
+
 	response = op->response->payload;
 	*result = response->result_code;
 	*signature_size = op->response->payload_size - sizeof(*response);
+	if (*signature_size > CAP_SIGNATURE_MAX_SIZE) {
+		dev_err(cap->parent, "authenticate signature too large (%u)\n",
+			*signature_size);
+		ret = -E2BIG;
+		goto done;
+	}
 	memcpy(auth_response, response->response, sizeof(response->response));
 	memcpy(signature, response->signature, *signature_size);
 
-- 
2.43.0