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Bound clipboard payloads and image parsing

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The capture daemon read the whole clipboard payload into memory and handed
it to Pillow, zbarimg and tesseract with no limit. Payloads now stream
through a capped reader (32 MiB images, 4 MiB text, 5 s deadline) and are
dropped when exceeded; image dimensions come from the container header
without decoding, and QR/OCR only run under 40 megapixels. The OCR backfill
script applies the same pixel guard. Limits are overridable via
CLIPBOARD_MAX_IMAGE_BYTES, CLIPBOARD_MAX_TEXT_BYTES, CLIPBOARD_MAX_PARSE_PIXELS.
This commit is contained in:
Alan
2026-09-08 15:20:10 +01:00
parent b1ebdb83e6
commit 4522fdbce1
3 changed files with 166 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files
capture.py
+148 -14
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@@ -11,12 +11,19 @@ the current clipboard. Emits exactly one JSON line per capture:
Sensitive clips (x-kde-passwordManagerHint / CLIPBOARD_STATE=sensitive) and
binary payloads are skipped silently.
The clipboard owner is untrusted: every payload is read through a bounded
reader (byte cap + deadline) and QR/OCR only run on images whose header
dimensions are under a pixel cap, so a hostile or runaway source cannot make
the plugin buffer an unbounded payload or decode a decompression bomb.
"""
import hashlib
import json
import os
import select
import shutil
import struct
import subprocess
import sys
import tempfile
@@ -34,6 +41,24 @@ IMAGE_EXT = {"image/png": "png", "image/jpeg": "jpg", "image/webp": "webp",
TEXT_TYPES = ["text/plain;charset=utf-8", "text/plain", "UTF8_STRING", "STRING", "TEXT", "COMPOUND_TEXT"]
def _env_int(name, default):
try:
return max(0, int(os.environ.get(name, "") or default))
except ValueError:
return default
# Payload limits. Anything larger is dropped (not truncated) so the history
# never holds a partial clip. Overridable per environment.
MAX_IMAGE_BYTES = _env_int("CLIPBOARD_MAX_IMAGE_BYTES", 32 * 1024 * 1024)
MAX_TEXT_BYTES = _env_int("CLIPBOARD_MAX_TEXT_BYTES", 4 * 1024 * 1024)
# QR decoding and OCR decode the full bitmap; skip them above this many
# pixels (the image is still recorded and previewed by Qt, which has its own
# allocation limits).
MAX_PARSE_PIXELS = _env_int("CLIPBOARD_MAX_PARSE_PIXELS", 40 * 1000 * 1000)
READ_TIMEOUT = 5.0
def run(args, timeout=5):
try:
r = subprocess.run(args, capture_output=True, timeout=timeout)
@@ -42,6 +67,115 @@ def run(args, timeout=5):
return None
def read_bounded(args, limit, timeout=READ_TIMEOUT):
"""Run `args` and return its stdout, or None if it exits non-zero, writes
more than `limit` bytes, or does not finish within `timeout` seconds.
Output is streamed and the process is killed as soon as the cap is hit,
so memory use is bounded by `limit` regardless of what the source sends."""
try:
proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL)
except Exception:
return None
chunks = []
total = 0
ok = True
deadline = time.monotonic() + timeout
try:
while True:
remaining = deadline - time.monotonic()
if remaining <= 0:
ok = False
break
ready, _, _ = select.select([proc.stdout], [], [], remaining)
if not ready:
ok = False
break
chunk = os.read(proc.stdout.fileno(), 65536)
if not chunk:
break
total += len(chunk)
if total > limit:
ok = False
break
chunks.append(chunk)
except Exception:
ok = False
finally:
if not ok:
proc.kill()
try:
proc.wait(timeout=2)
except Exception:
proc.kill()
proc.stdout.close()
if not ok or proc.returncode != 0:
return None
return b"".join(chunks)
def read_clipboard(mime, limit):
return read_bounded(["wl-paste", "--type", mime, "--no-newline"], limit)
def image_size(data, mime):
"""(width, height) from the container header alone — no pixel decoding.
Returns None when the header is not understood."""
try:
if mime == "image/png" and data[:8] == b"\x89PNG\r\n\x1a\n" and data[12:16] == b"IHDR":
return struct.unpack(">II", data[16:24])
if mime == "image/gif" and data[:6] in (b"GIF87a", b"GIF89a"):
return struct.unpack("<HH", data[6:10])
if mime == "image/bmp" and data[:2] == b"BM":
w, h = struct.unpack("<ii", data[18:26])
return abs(w), abs(h)
if mime == "image/webp" and data[:4] == b"RIFF" and data[8:12] == b"WEBP":
chunk = data[12:16]
if chunk == b"VP8X":
w = int.from_bytes(data[24:27], "little") + 1
h = int.from_bytes(data[27:30], "little") + 1
return w, h
if chunk == b"VP8L" and data[20] == 0x2F:
bits = int.from_bytes(data[21:25], "little")
return (bits & 0x3FFF) + 1, ((bits >> 14) & 0x3FFF) + 1
if chunk == b"VP8 ":
w, h = struct.unpack("<HH", data[26:30])
return w & 0x3FFF, h & 0x3FFF
if mime == "image/jpeg" and data[:2] == b"\xff\xd8":
i = 2
n = len(data)
while i + 9 < n:
if data[i] != 0xFF:
i += 1
continue
marker = data[i + 1]
if marker in (0xD8, 0x01) or 0xD0 <= marker <= 0xD7:
i += 2
continue
length = struct.unpack(">H", data[i + 2:i + 4])[0]
if marker in (0xC0, 0xC1, 0xC2, 0xC3, 0xC5, 0xC6, 0xC7, 0xC9, 0xCA, 0xCB, 0xCD, 0xCE, 0xCF):
h, w = struct.unpack(">HH", data[i + 5:i + 9])
return w, h
i += 2 + length
if mime == "image/tiff" and data[:4] in (b"II*\x00", b"MM\x00*"):
end = "<" if data[:2] == b"II" else ">"
off = struct.unpack(end + "I", data[4:8])[0]
count = struct.unpack(end + "H", data[off:off + 2])[0]
w = h = None
for k in range(min(count, 64)):
e = off + 2 + k * 12
tag, typ = struct.unpack(end + "HH", data[e:e + 4])
val = struct.unpack(end + ("H" if typ == 3 else "I"), data[e + 8:e + 8 + (2 if typ == 3 else 4)])[0]
if tag == 256:
w = val
elif tag == 257:
h = val
if w and h:
return w, h
except Exception:
return None
return None
def list_types():
out = run(["wl-paste", "--list-types"])
if not out:
@@ -86,22 +220,22 @@ def capture_image(types, app):
mime = next((m for m in IMAGE_MIMES if m in types), None)
if not mime:
return
data = run(["wl-paste", "--type", mime, "--no-newline"])
data = read_clipboard(mime, MAX_IMAGE_BYTES)
if not data:
return
# Oversized, slow, or empty: skip the clip entirely (an image mime was
# offered, so we do not fall through to a text capture of it either).
return True
os.makedirs(IMAGE_DIR, exist_ok=True)
digest = hashlib.sha256(data).hexdigest()
path = os.path.join(IMAGE_DIR, f"{digest}.{IMAGE_EXT[mime]}")
entry = {"type": "image", "mime": mime, "path": path, "bytes": len(data), "app": app}
# Dimensions via Pillow when available; harmless without it.
try:
from PIL import Image # noqa: PLC0415
import io # noqa: PLC0415
with Image.open(io.BytesIO(data)) as im:
entry["w"], entry["h"] = im.size
except Exception:
pass
# Dimensions from the header only; the bitmap is never decoded here.
size = image_size(data, mime)
if size:
entry["w"], entry["h"] = int(size[0]), int(size[1])
# Unknown or huge dimensions → no QR/OCR pass (both decode the full image).
parse_ok = bool(size) and size[0] * size[1] <= MAX_PARSE_PIXELS
if not os.path.exists(path):
fd, tmp = tempfile.mkstemp(dir=IMAGE_DIR)
@@ -116,11 +250,11 @@ def capture_image(types, app):
pass
return
qr = decode_qr(path) if os.environ.get("CLIPBOARD_QR", "1") != "0" else None
qr = decode_qr(path) if parse_ok and os.environ.get("CLIPBOARD_QR", "1") != "0" else None
if qr:
entry["qr"] = qr
ocr = decode_ocr(path, os.environ.get("CLIPBOARD_OCR_LANG", "eng"))
ocr = decode_ocr(path, os.environ.get("CLIPBOARD_OCR_LANG", "eng")) if parse_ok else None
if ocr:
entry["ocr"] = ocr
@@ -175,7 +309,7 @@ def decode_ocr(path, lang):
def capture_uri_list(types, app):
if "text/uri-list" not in types:
return False
data = run(["wl-paste", "--type", "text/uri-list", "--no-newline"])
data = read_clipboard("text/uri-list", MAX_TEXT_BYTES)
if not data:
return False
text = decode_text(data)
@@ -200,7 +334,7 @@ def capture_text(types, app):
mime = next((m for m in TEXT_TYPES if m in types), None)
if not mime:
return
data = run(["wl-paste", "--type", mime, "--no-newline"])
data = read_clipboard(mime, MAX_TEXT_BYTES)
if not data:
return
text = decode_text(data)