SIGSEGV in TextIOWrapper.readline() after seek() with cookie containing negative chars_to_skip
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interpreter-core
type-crash
- Dominant language
- Python
- Stars
- 77.2k
- Forks
- 35.9k
- PR merge metrics
- PR metrics pending
Description
Crash report
What happened?
import io, sys
COOKIE_VALUE = (100 << (12 * 8)) | (0x80 << (19 * 8))
data = b"Hello World!" * 100
raw = io.BytesIO(data)
buf = io.BufferedReader(raw)
tio = io.TextIOWrapper(buf, encoding='utf-8')
tio.read(20)
tio.seek(COOKIE_VALUE)
tio.readline()
sys.exit(0)
CPython versions tested on:
3.16
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.16.0a0 (tags/v3.15.0b1-959-gd0714388278:d0714388278, Jul 13 2026, 20:32:55) [GCC 12.3.0] Linux x86_64, GCC 12.3.0
Linked PRs
- gh-153667
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the supplied Python reproducer on Linux and inspect the io.TextIOWrapper seek() and readline() entry points involved in the crash. Done means the same cookie no longer causes a SIGSEGV and the reproducer exits normally; review linked PR gh-153667 before starting because work may already be underway.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- backend
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100