Message-ID: <gh-postgresql-interfaces-psqlodbc-175@github.com>
From: "jarvis24young (@jarvis24young)" <noreply+jarvis24young@github.com>
To: "postgresql-interfaces/psqlodbc" <noreply+postgresql-interfaces-psqlodbc@github.com>
Date: Thu, 23 Apr 2026 09:07:37 +0000
Subject: [postgresql-interfaces/psqlodbc] PR #175: Validate percent escapes before decoding connection-string values
List-Id: <gh-postgresql-interfaces-psqlodbc.github.com>
X-GitHub-Author-Id: 48787405
X-GitHub-Author-Login: jarvis24young
X-GitHub-Issue: 175
X-GitHub-Repo: postgresql-interfaces/psqlodbc
X-GitHub-State: merged
X-GitHub-Type: pull_request
X-GitHub-Url: https://github.com/postgresql-interfaces/psqlodbc/pull/175
Content-Type: text/plain; charset=utf-8

This fixes sanitizer-detected undefined behavior in connection-string percent decoding.

Root cause:
- `decode()` treated every `%` in a connection-string value as the beginning of a `%xx` percent escape.
- It called `conv_from_hex(&in[i])` without first checking that two following hex digits were present.
- For a truncated value such as `pqopt=application_name=%`, `conv_from_hex()` reads the string terminator, computes a negative value, and left-shifts it. UBSan reports this as undefined behavior.

Fix:
- Decode only valid `%xx` escapes where both following characters are hex digits.
- Leave malformed or truncated percent sequences unchanged, preserving compatibility while avoiding undefined behavior.

Regression test:
- Adds `percent-decode-test`, which exercises the public `SQLDriverConnect()` path with `pqopt=application_name=%`, `%A`, `%G1`, and `%20`.
- The test requires `SQLDriverConnect()` to succeed for each case, so it verifies more than just "no crash".

Verification performed under ASan/UBSan:

```bash
cd ~/psqlodbc-build/test
export LD_PRELOAD=/usr/lib/gcc/x86_64-linux-gnu/13/libasan.so
ODBCSYSINI=. ODBCINSTINI=./odbcinst.ini ODBCINI=./odbc.ini \
ASAN_OPTIONS=halt_on_error=1:abort_on_error=1 \
UBSAN_OPTIONS=halt_on_error=1:print_stacktrace=1 \
./exe/percent-decode-test
```

Output:

```text
truncated percent: ok
one hex digit: ok
non-hex escape: ok
valid percent escape: ok
```