Description

aminghadersohi

opened on Sep 26, 2026

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Summary

On the 1.x line (tested with firebird-driver 1.10.11 / firebird-base 1.8.0), letting the garbage collector finalize a Connection that was never closed segfaults the Python process. This is the same crash as #69. #72 fixed it on master on 2026-05-21, but that fix is not on release-1.x, and it is also not in any 2.x release yet (2.0.3 was published 2026-04-20).

On 1.x, iAttachment.detach() (the v5 override in interfaces.py) calls the native detach without the if self._refcnt: guard that iAttachment_v4.detach() has. During cyclic garbage collection the interface can be released first, and Connection.__del__ then detaches freed memory.

Minimal reproduction

Firebird 5.0.3 server, CPython 3.11.15, Linux x86_64, firebird-driver 1.10.11:

import gc, os, sys
from firebird.driver import connect, driver_config

driver_config.fb_client_library.value = os.environ["FB_CLIENT_LIBRARY"]
DSN, PASSWORD = os.environ["FB_DSN"], os.environ["FB_PASSWORD"]

def abandon():
    con = connect(DSN, user="SYSDBA", password=PASSWORD)
    cur = con.cursor()
    cur.execute("select count(*) from rdb$relations")
    cur.fetchall()
    # no con.close(): the connection is left to the garbage collector

for i in range(100):
    abandon()
    gc.collect()
print("completed without crash")

Output (python -X faulthandler repro.py), 3 of 3 runs, exit code 139:

Fatal Python error: Segmentation fault

  File ".../firebird/driver/interfaces.py", line 1236 in detach
  File ".../firebird/driver/core.py", line 1672 in __del__
  File "repro.py", line 18 in <module>

With the #69 guard applied to release-1.x (if self._refcnt: around the native detach in the v5 iAttachment.detach()), the same script completes 100 iterations without a crash in 3 of 3 runs.

Impact

Any unclosed connection can crash the process when it is garbage collected. Examples include a connection pool that drops a connection it failed to close (a SQLAlchemy dialect whose terminate hook fails on invalidation), or application code that forgets close(). Applications that cannot move to 2.x yet (2.x requires firebird-base~=2.0 → protobuf~=5.29) are stuck on 1.10.11.

Request

1. Backport the segfault in garbage collecting #69 guard to release-1.x and publish a 1.10.x release. A backport PR follows.
2. If possible, publish a 2.x release that includes Fix segfault in garbage collection of abandoned connection (#69) #72.

Activity

1. aminghadersohi commented on Sep 26, 2026

   

   aminghadersohi

   on Sep 26, 2026

   Author

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   Follow-up: the detach() guard from #72 / #78 fixes Connection.__del__ → iAttachment.detach(), but other finalization orders in the same cycle still crash on 1.10.11.

   When the attachment's own iReferenceCounted.__del__ releases it first, the remaining finalizers still call into its children. For example, Cursor.__del__ → Cursor.close() → iResultSet.close() calls into a result set whose attachment is already gone. Guarding on the wrapper's own _refcnt doesn't catch this, because the result set wrapper still holds its reference.

   Minimal reproduction (Firebird 5.0.3, CPython 3.11, firebird-driver 1.10.11 with the #78 change applied):

   import gc
   from firebird.driver import connect
   
   def abandon():
       con = connect(DSN, user="SYSDBA", password=PASSWORD)
       cur = con.cursor()
       cur.execute("select rdb$relation_id from rdb$relations")
       cur.fetchone()            # result set left open
       con.cycle = [con, cur]    # force collection by the cyclic GC
       cur.cycle = con
   
   for _ in range(100):
       abandon()
       gc.collect()

   This segfaults in interfaces.py iResultSet.close (via Cursor.__del__). An open BlobReader, or an active TransactionManager with a prepared statement, crashes the same way.

   A fix that covers all orders: while a garbage collection is running, defer every native call that releases an interface (release, detach, commit, rollback, close, free, cancel). Then replay those calls right after the collection, children first: result sets and blobs, then statements, then transactions, then attachments. This can hook gc.callbacks. With that change, the scenarios above run 100 iterations without a crash on Firebird 3.0.14, 4.0.7 and 5.0.3, and leave no server attachments behind.
2. pcisar

   added a commit that references this issue on Oct 7, 2026

   Guard iAttachment.detach() against an already-released interface (1.x)

   This issue will close once commit 375055e is merged into the 'master' branch.

   375055e

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