[PATCH v9 1/6] Bluetooth: btmtk: Add firmware size validation in btmtk_setup_firmware_79xx()

[Chris Lu <chris.lu@mediatek.com>]

Add firmware size validation to prevent out-of-bounds access when loading
truncated or malicious firmware files.

Add three levels of validation:
1. Minimum size check for header and global descriptor
2. Section map bounds check with integer overflow protection using
   check_mul_overflow() and check_add_overflow()
3. Section data bounds check before accessing each section

This matches the validation approach used in btmtk_load_cbmcu_firmware().

Signed-off-by: Chris Lu <chris.lu@mediatek.com>
Assisted-by: Claude:Sonnet-4.5
---
 drivers/bluetooth/btmtk.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/drivers/bluetooth/btmtk.c b/drivers/bluetooth/btmtk.c
index 02a96342e964..3491060b3ae9 100644
--- a/drivers/bluetooth/btmtk.c
+++ b/drivers/bluetooth/btmtk.c
@@ -145,6 +145,7 @@ int btmtk_setup_firmware_79xx(struct hci_dev *hdev, const char *fwname,
 	int err, dlen, i, status;
 	u8 flag, first_block, retry;
 	u32 section_num, dl_size, section_offset;
+	size_t expected_size;
 	u8 cmd[64];
 
 	err = request_firmware(&fw, fwname, &hdev->dev);
@@ -153,12 +154,40 @@ int btmtk_setup_firmware_79xx(struct hci_dev *hdev, const char *fwname,
 		return err;
 	}
 
+	/* Validate minimum firmware size for header and global descriptor */
+	if (fw->size < MTK_FW_ROM_PATCH_HEADER_SIZE + MTK_FW_ROM_PATCH_GD_SIZE) {
+		bt_dev_err(hdev, "Firmware file too small: size=%zu, expected at least %u bytes",
+			   fw->size, MTK_FW_ROM_PATCH_HEADER_SIZE + MTK_FW_ROM_PATCH_GD_SIZE);
+		err = -EINVAL;
+		goto err_release_fw;
+	}
+
 	fw_ptr = fw->data;
 	fw_bin_ptr = fw_ptr;
 	hdr = (struct btmtk_patch_header *)fw_ptr;
 	globaldesc = (struct btmtk_global_desc *)(fw_ptr + MTK_FW_ROM_PATCH_HEADER_SIZE);
 	section_num = le32_to_cpu(globaldesc->section_num);
 
+	/* Check for potential integer overflow in size calculation */
+	if (check_mul_overflow((size_t)MTK_FW_ROM_PATCH_SEC_MAP_SIZE,
+			       (size_t)section_num, &expected_size) ||
+	    check_add_overflow(expected_size,
+			       (size_t)(MTK_FW_ROM_PATCH_HEADER_SIZE +
+					MTK_FW_ROM_PATCH_GD_SIZE),
+			       &expected_size)) {
+		bt_dev_err(hdev, "Firmware size calculation overflow (section_num=%u)",
+			   section_num);
+		err = -EINVAL;
+		goto err_release_fw;
+	}
+
+	if (fw->size < expected_size) {
+		bt_dev_err(hdev, "Firmware truncated: size=%zu, expected=%zu (section_num=%u)",
+			   fw->size, expected_size, section_num);
+		err = -EINVAL;
+		goto err_release_fw;
+	}
+
 	bt_dev_info(hdev, "HW/SW Version: 0x%04x%04x, Build Time: %s",
 		    le16_to_cpu(hdr->hwver), le16_to_cpu(hdr->swver), hdr->datetime);
 
@@ -171,6 +200,16 @@ int btmtk_setup_firmware_79xx(struct hci_dev *hdev, const char *fwname,
 		section_offset = le32_to_cpu(sectionmap->secoffset);
 		dl_size = le32_to_cpu(sectionmap->bin_info_spec.dlsize);
 
+		/* Validate section boundaries to prevent out-of-bounds access */
+		if (dl_size > 0 &&
+		    (section_offset > fw->size ||
+		     dl_size > fw->size - section_offset)) {
+			bt_dev_err(hdev, "Section %d out of bounds: offset=%u, size=%u, fw_size=%zu",
+				   i, section_offset, dl_size, fw->size);
+			err = -EINVAL;
+			goto err_release_fw;
+		}
+
 		/* MT6639: only download sections where dlmode byte0 == 0x01,
 		 * matching the Windows driver behavior which skips WiFi/other
 		 * sections that would cause the chip to hang.
-- 
2.45.2