From 881d670b54f3d25cd5b8f31efa72adbf3c48dcda Mon Sep 17 00:00:00 2001
From: Pol Henarejos <pol.henarejos@cttc.es>
Date: Fri, 14 Aug 2026 19:45:23 +0200
Subject: [PATCH] Reject truncated data object responses

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>
---
 src/openpgp/cmd_get_data.c    | 9 +++++++--
 src/openpgp/cmd_put_data.c    | 3 +++
 src/openpgp/files.c           | 4 ++--
 src/openpgp/files.h           | 1 +
 tests/card_test_empty_card.py | 2 +-
 5 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/openpgp/cmd_get_data.c b/src/openpgp/cmd_get_data.c
index 3a92ef3..56cea80 100644
--- a/src/openpgp/cmd_get_data.c
+++ b/src/openpgp/cmd_get_data.c
@@ -66,6 +66,9 @@ int cmd_get_data(void) {
     else {
         select_file(ef);
     }
+    if ((file_get_type(ef) & FILE_DATA_FLASH) && file_get_size(ef) > OPENPGP_MAX_DO_SIZE) {
+        return SW_MEMORY_FAILURE();
+    }
     if (ef->data) {
         if (requested_fid == EF_PW_STATUS || requested_fid == EF_HIST_BYTES ||
             requested_fid == EF_FULL_AID || requested_fid == EF_SEC_TPL) {
@@ -73,7 +76,6 @@ int cmd_get_data(void) {
         }
         uint16_t fids[] = { 1, ef->fid };
         uint16_t data_len = parse_do(fids, 1);
-        data_len = MIN(data_len, res_APDU_size);
         if (!(file_get_type(ef) & FILE_DATA_FLASH)) {
             uint8_t *p = NULL;
             tlv_item_t item;
@@ -105,7 +107,10 @@ int cmd_get_data(void) {
             if (data_len >= 256) {
                 off++;
             }
-            data_len = MIN(data_len, OPENPGP_MAX_RESPONSE_SIZE - off);
+            if (data_len > OPENPGP_MAX_RESPONSE_SIZE - off) {
+                res_APDU_size = 0;
+                return SW_MEMORY_FAILURE();
+            }
             res_APDU_size = data_len;
             memmove(res_APDU + off, res_APDU, data_len);
             off = 0;
diff --git a/src/openpgp/cmd_put_data.c b/src/openpgp/cmd_put_data.c
index ceb6a10..f2722d6 100644
--- a/src/openpgp/cmd_put_data.c
+++ b/src/openpgp/cmd_put_data.c
@@ -51,6 +51,9 @@ int cmd_put_data(void) {
     if (!put_data_authorized(requested_fid)) {
         return SW_SECURITY_STATUS_NOT_SATISFIED();
     }
+    if (apdu.nc > OPENPGP_MAX_DO_SIZE) {
+        return SW_WRONG_DATA();
+    }
 
     uint16_t max_size = fixed_do_max_size(requested_fid);
     if (max_size != 0 && apdu.nc > max_size) {
diff --git a/src/openpgp/files.c b/src/openpgp/files.c
index 54ca13f..e0d2fe6 100644
--- a/src/openpgp/files.c
+++ b/src/openpgp/files.c
@@ -60,8 +60,8 @@ uint8_t extended_capabilities[] = {
                      */
     0,        /* Secure Messaging Algorithm: N/A (TDES=0, AES=1) */
     (uint8_t)(OPENPGP_MAX_CHALLENGE_SIZE >> 8), (uint8_t)OPENPGP_MAX_CHALLENGE_SIZE, /* Max size of GET CHALLENGE */
-    0x08, 0x00,   /* max. length of cardholder certificate (2KiB) */
-    0x08, 0x00,   /* max. length of private DO (2KiB) */
+    (uint8_t)(OPENPGP_MAX_DO_SIZE >> 8), (uint8_t)OPENPGP_MAX_DO_SIZE,
+    (uint8_t)(OPENPGP_MAX_DO_SIZE >> 8), (uint8_t)OPENPGP_MAX_DO_SIZE,
     0x00, 0x1
 };
 
diff --git a/src/openpgp/files.h b/src/openpgp/files.h
index fa2f584..a4cc774 100644
--- a/src/openpgp/files.h
+++ b/src/openpgp/files.h
@@ -89,6 +89,7 @@
 #define EF_GFM          0x7f74 //C
 
 #define OPENPGP_MAX_CHALLENGE_SIZE 1024u
+#define OPENPGP_MAX_DO_SIZE        2036u
 
 // PIV
 
diff --git a/tests/card_test_empty_card.py b/tests/card_test_empty_card.py
index dbc7c5d..1fd24ee 100644
--- a/tests/card_test_empty_card.py
+++ b/tests/card_test_empty_card.py
@@ -201,7 +201,7 @@ def test_extended_capabilities(card):
         pytest.skip("Yubikey returns 6B00 when no key")
     else:
         a = get_data_object(card, 0xc0)
-        assert a == None or match(b'[\x70\x7F\x75\x77]\x00(?:\x00.|\x04\x00)[\x00\x08]\x00\x08\x00[\x00\x01][\x00\x01]', a)
+        assert a == None or match(b'[\x70\x7F\x75\x77]\x00(?:\x00.|\x04\x00)(?:[\x00\x08]\x00|\x07\xf4)(?:\x08\x00|\x07\xf4)[\x00\x01][\x00\x01]', a)
 
 def test_key_attributes_1(card):
     if card.is_yubikey: