The patch attached (a one-liner) includes information about how to reproduce the issue and why it happens.
We applied it to our production servers (9.5) and has been working as expected for a while. I've also checked that it can be applied cleanly to current master. Could it make its way into master? maybe 9.5 and 9.6 as well? Thanks! -- Rafa de la Torre rto...@carto.com
From e95649d8d173f483d67d9338a9089947a7667e5f Mon Sep 17 00:00:00 2001 From: Rafa de la Torre <rto...@cartodb.com> Date: Wed, 23 Nov 2016 10:50:40 +0100 Subject: [PATCH] Fix segfault in plpython's exception handling When a subtransaction is aborted in plpython because of an SPI exception, it tries to find a matching python exception in a hash `PLy_spi_exceptions` and to make python vm raise it. That hash is generated during module initialization, but the exception objects are not marked to prevent the garbage collector from collecting them, which can lead to a segmentation fault when processing any SPI exception. PoC to reproduce the issue: ```sql CREATE OR REPLACE FUNCTION server_crashes() RETURNS VOID AS $$ import gc gc.collect() plan = plpy.prepare('SELECT raises_an_spi_exception();', []) plpy.execute(plan) $$ LANGUAGE plpythonu; CREATE OR REPLACE FUNCTION raises_an_spi_exception() RETURNS VOID AS $$ DECLARE sql TEXT; BEGIN sql = format('%I', NULL); -- NullValueNotAllowed END $$ LANGUAGE plpgsql; SELECT server_crashes(); -- segfault here ``` Stacktrace of the problem (using PostgreSQL `REL9_5_STABLE` and python `2.7.3-0ubuntu3.8` on a Ubuntu 12.04): ``` Program received signal SIGSEGV, Segmentation fault. 0x00007f3155c7670b in PyObject_Call (func=0x7f31b7db2a30, arg=0x7f31b87d17d0, kw=0x0) at ../Objects/abstract.c:2525 2525 ../Objects/abstract.c: No such file or directory. (gdb) bt #0 0x00007f3155c7670b in PyObject_Call (func=0x7f31b7db2a30, arg=0x7f31b87d17d0, kw=0x0) at ../Objects/abstract.c:2525 #1 0x00007f3155d81ab1 in PyEval_CallObjectWithKeywords (func=0x7f31b7db2a30, arg=0x7f31b87d17d0, kw=0x0) at ../Python/ceval.c:3890 #2 0x00007f3155c766ed in PyObject_CallObject (o=0x7f31b7db2a30, a=0x7f31b87d17d0) at ../Objects/abstract.c:2517 #3 0x00007f31561e112b in PLy_spi_exception_set (edata=0x7f31b8743d78, excclass=0x7f31b7db2a30) at plpy_spi.c:547 #4 PLy_spi_subtransaction_abort (oldcontext=<optimized out>, oldowner=<optimized out>) at plpy_spi.c:527 #5 0x00007f31561e2185 in PLy_spi_execute_plan (ob=0x7f31b87d0cd8, list=0x7f31b7c530d8, limit=0) at plpy_spi.c:307 #6 0x00007f31561e22d4 in PLy_spi_execute (self=<optimized out>, args=0x7f31b87a6d08) at plpy_spi.c:180 #7 0x00007f3155cda4d6 in PyCFunction_Call (func=0x7f31b7d29600, arg=0x7f31b87a6d08, kw=0x0) at ../Objects/methodobject.c:81 #8 0x00007f3155d82383 in call_function (pp_stack=0x7fff9207e710, oparg=2) at ../Python/ceval.c:4021 #9 0x00007f3155d7cda4 in PyEval_EvalFrameEx (f=0x7f31b8805be0, throwflag=0) at ../Python/ceval.c:2666 #10 0x00007f3155d82898 in fast_function (func=0x7f31b88b5ed0, pp_stack=0x7fff9207ea70, n=0, na=0, nk=0) at ../Python/ceval.c:4107 #11 0x00007f3155d82584 in call_function (pp_stack=0x7fff9207ea70, oparg=0) at ../Python/ceval.c:4042 #12 0x00007f3155d7cda4 in PyEval_EvalFrameEx (f=0x7f31b8805a00, throwflag=0) at ../Python/ceval.c:2666 #13 0x00007f3155d7f8a9 in PyEval_EvalCodeEx (co=0x7f31b88aa460, globals=0x7f31b8727ea0, locals=0x7f31b8727ea0, args=0x0, argcount=0, kws=0x0, kwcount=0, defs=0x0, defcount=0, closure=0x0) at ../Python/ceval.c:3253 #14 0x00007f3155d74ff4 in PyEval_EvalCode (co=0x7f31b88aa460, globals=0x7f31b8727ea0, locals=0x7f31b8727ea0) at ../Python/ceval.c:667 #15 0x00007f31561dc476 in PLy_procedure_call (kargs=kargs@entry=0x7f31561e5690 "args", vargs=<optimized out>, proc=0x7f31b873b2d0, proc=0x7f31b873b2d0) at plpy_exec.c:801 #16 0x00007f31561dd9c6 in PLy_exec_function (fcinfo=fcinfo@entry=0x7f31b7c1f870, proc=0x7f31b873b2d0) at plpy_exec.c:61#17 0x00007f31561de9f9 in plpython_call_handler (fcinfo=0x7f31b7c1f870) at plpy_main.c:291 ``` --- src/pl/plpython/plpy_plpymodule.c | 1 + 1 file changed, 1 insertion(+) diff --git a/src/pl/plpython/plpy_plpymodule.c b/src/pl/plpython/plpy_plpymodule.c index a44b7fb..3334739 100644 --- a/src/pl/plpython/plpy_plpymodule.c +++ b/src/pl/plpython/plpy_plpymodule.c @@ -258,6 +258,7 @@ PLy_generate_spi_exceptions(PyObject *mod, PyObject *base) PyDict_SetItemString(dict, "sqlstate", sqlstate); Py_DECREF(sqlstate); exc = PyErr_NewException(exception_map[i].name, base, dict); + Py_INCREF(exc); PyModule_AddObject(mod, exception_map[i].classname, exc); entry = hash_search(PLy_spi_exceptions, &exception_map[i].sqlstate, HASH_ENTER, &found);
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