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test: raise the coverage of the TFTP and FTP servers past 81% - #125
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- The message of a refused operation was handed to the error as a second argument, so the peer read a pair of raw values instead of it - A file served under an absolute name left the name of it unbound - The module goes from 25.7% to 97.6%
- A name that walked out of the root reached any file of the machine, the containment that the file server already does was missing here - The module goes from 27.1% to 66.8% and the package to 81.4% - The floor of the job goes from 79 to 80
📝 WalkthroughWalkthroughThe change secures FTP and TFTP paths, formats TFTP errors, adds extensive FTP and TFTP tests, records the fixes in the changelog, and raises the coverage threshold from 79% to 80%. ChangesFTP path security and connection behavior
TFTP protocol behavior
Coverage threshold
Merge Risk: 🟠 High · up to The PR blocks ordinary 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 77 functions across 4 files. (1 skipped: 1 unsupported.)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
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- A system that locks an open file would not let the temporary root go, which broke the cases of the transfers under Windows
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🟡 Changes recommended
The new FTP path containment check uses a string-prefix match that can still be bypassed by sibling-prefix paths (eg /srv/ftp-old).
Once you've addressed the issues Copilot identified, you can request another Copilot review.
Pull request overview
Improves overall package test coverage past the CI floor by adding substantial unit coverage for the TFTP and FTP server implementations, and includes a few bug/security fixes uncovered while writing those tests.
Changes:
- Add comprehensive TFTP server/session/request test coverage and expand FTP server/connection coverage.
- Fix TFTP error formatting and absolute-path handling in
TFTPSession._get_file. - Add a containment check in
FTPConnection._get_path, update changelog entries, and raise the CI coverage floor to 80%.
File summaries
| File | Description |
|---|---|
| src/netius/test/servers/tftp.py | New test module covering TFTP session, request parsing, and server error/response paths. |
| src/netius/test/servers/ftp.py | Expanded FTP server/connection test coverage, including path traversal and file ops paths. |
| src/netius/servers/tftp.py | Fixes TFTP absolute-name handling and formats invalid-operation errors as proper messages. |
| src/netius/servers/ftp.py | Adds path containment enforcement for FTP filesystem operations. |
| CHANGELOG.md | Documents the TFTP and FTP fixes. |
| .github/workflows/main.yml | Raises coverage fail-under threshold from 79 to 80. |
Review details
- Files reviewed: 6/6 changed files
- Comments generated: 1
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Inline comments:
In `@CHANGELOG.md`:
- Around line 23-30: Update CHANGELOG.md by moving all non-empty Unreleased
entries into a new dated semantic-version section, then recreate empty Added,
Changed, and Fixed subsections under Unreleased. Create the corresponding GitHub
release using the new version and matching changelog entry.
In `@src/netius/servers/ftp.py`:
- Around line 500-502: Update the path validation around relative_path to
resolve both self.base_path and the candidate path, then enforce component-aware
containment rather than string startswith; reject sibling prefixes and paths
escaping through external symlinks. Add regression coverage for both invalid
cases while preserving valid descendants.
In `@src/netius/test/servers/ftp.py`:
- Line 131: Update the None comparisons in the relevant FTP test server code,
including the checks near the visible mock condition and the corresponding check
near line 502, to use identity checks with is None instead of equality
comparisons.
In `@src/netius/test/servers/tftp.py`:
- Line 239: Close self.session before shutil.rmtree(self.base) in
src/netius/test/servers/tftp.py lines 239-239. Also close every session in
self.server.sessions, or make the server cleanup perform this, before
shutil.rmtree(self.base) at lines 377-377.
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.github/workflows/main.ymlCHANGELOG.mdsrc/netius/servers/ftp.pysrc/netius/servers/tftp.pysrc/netius/test/servers/ftp.pysrc/netius/test/servers/tftp.py
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🟡 Changes recommended
FTP sibling-prefix traversal and TFTP parent traversal still permit access outside their configured roots.
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Review details
Suppressed comments (1)
src/netius/servers/ftp.py:500
startswithis not a path-component check, so the traversal remains exploitable whenever a sibling shares the root prefix. For example, a root/srv/ftpaccepts../ftp-old/secretbecause/srv/ftp-old/secret.startswith(/srv/ftp) is true. Compare against the root itself or the root plus a separator, and add this sibling-prefix case to the regression test.
is_sub = relative_path.startswith(self.base_path)
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netius/src/netius/test/servers/ftp.py
Line 22 in 85de56b
Add the required FTP test module docstring
This newly added test module reaches __author__ without a module-level docstring. Add a docstring before this assignment whose first line starts with the dotted module name and a short description, as required for every Python module.
AGENTS.md reference: AGENTS.md:L137-L138
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Reviewed by Cursor Bugbot for commit 85de56b. Configure here.
- A TFTP read request walked out of the root and served any file, the trimming of the leading separator does nothing to a name that steps up - A sibling whose name only starts like the root passed the FTP check
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Inline comments:
In `@src/netius/servers/tftp.py`:
- Around line 111-121: Update the path resolution in the TFTP filename
validation to apply os.path.realpath to both base_path and the constructed path
before the containment check, preserving the existing SecurityError for paths
outside the resolved base directory.
Apply the same fix in `@src/netius/servers/ftp.py` around lines 500 - 502: The
same lexical-only containment issue applies to FTP operations.
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CHANGELOG.mdsrc/netius/servers/ftp.pysrc/netius/servers/tftp.pysrc/netius/test/servers/ftp.pysrc/netius/test/servers/tftp.py
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Raises the package past 81% by covering the two modules that were furthest behind, and fixes the four bugs that writing those cases exposed, two of them arbitrary file reads.
servers/tftp.pyservers/ftp.pyThe package figure above is a single Linux run. The combined one across the three platforms that the job measures, which is what the gate reads, lands at 81.0% (from 79.5%). The floor of the job goes from 79 to 80, one point under the combined figure, leaving the same headroom it has carried on every previous raise.
servers/tftp.pyhad no test module at all. It gains one covering the session, the request and the service, in the declaration order of each.An FTP peer could read any file on the machine
FTPConnection._get_pathjoins the name a peer sends onto the root that is served, normalises it, and hands it straight back:Every command that names a file goes through it, so
RETR,DELE,SIZE,MDTM,MKD,RMDandRNFR/RNTOall reached outside the root.This is a plain oversight rather than a design choice, and the code says so itself: the absolute branch deliberately strips the leading separator so that
/etc/passwdresolves to/srv/ftp/etc/passwdand stays contained. Only the relative..case was left unguarded.The fix is the containment the author already wrote for the sibling file server in
extra/file.py:550, applied verbatim so the two read alike:The check is taken at the boundary of the component rather than as a plain prefix, so a sibling root whose name merely starts the same way (
/srv/ftpagainst/srv/ftp-backup) is refused too:os.path.join(base, "")is used rather thanbase + os.sepso that a root of/keeps working, and the equality covers the resolution of the working directory itself. Symlinks are resolved the same wayextra/file.pyresolves them, lexically:realpathwould have to be applied to both sides or every path breaks where the root is itself reached through a link, and no command either service exposes can create one.CWD ..from the root now raises instead of answering 550; from any deeper directory it resolves normally.A TFTP peer could read any file on the machine
The same class of issue, and the worse of the two, since TFTP is unauthenticated UDP.
TFTPSession._get_fileonly trimmed a leading separator, which does nothing to a name that steps up, and never resolved the result at all. Driving it through the wire path rather than calling the method directly:It now resolves the candidate and takes the same containment as the FTP service.
Two more TFTP bugs
The error packet carried raw values instead of a message.
on_data_tftphanded the operation to the exception as a second argument rather than formatting it in, andon_error_tftpputsstr(exception)on the wire, so a peer that asked for an unsupported operation received:Every other
NetiusErrorin the package builds its message with%first. Now this one does too.A file served under an absolute name never opened.
TFTPSession._get_filebindsnameonly insideif not allow_absolute:, so calling it with the parameter the signature offers raisedUnboundLocalError: local variable 'name' referenced before assignment. The name is now read before the branch that trims it.Verification
All three traversal cases and both of the other TFTP cases fail against
masterand pass here.New cases probe the error paths rather than the happy one: removing a file twice, creating a directory that exists, renaming a source that is gone, entering a directory that is not there, listing a working directory that does not exist, a transfer whose file fits in a single block (so the acknowledge correctly has nothing left to answer), an operation the protocol does not name, and a request payload with no terminating null.
Checked on Python 3.14 (2009 passed, coverage gate and
mypy.stubtestclean), and on 3.6, 3.5 and 2.7 throughpython setup.py testas the job runs it, plusblack --checkacross 366 files.The first push failed on Windows: two cases held a session on the test case itself, so the file it was reading stayed open and the temporary root could not be removed. The sessions are now released in the teardown, which is what the service does with them anyway. The cases that keep a session local passed only because CPython refcounting closed the file for them, so those were given the same treatment rather than left to luck on a runtime that collects later.