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Commitc6f7f11

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Fix edge-case resource leaks in PL/Python error reporting.
PLy_elog_impl and its subroutine PLy_traceback intended to avoidleaking any PyObject reference counts, but their coverage of thematter was sadly incomplete. In particular, out-of-memory errorsin most of the string-construction subroutines could lead toreference count leaks, because those calls were outside thePG_TRY blocks responsible for dropping reference counts.Fix by (a) adjusting the scopes of the PG_TRY blocks, and(b) moving the responsibility for releasing the reference countsof the traceback-stack objects to PLy_elog_impl. This requiressome additional "volatile" markers, but not too many.In passing, fix an ancient thinko: use of the "e_module_o" PyObjectwas guarded by "if (e_type_s)", where surely "if (e_module_o)"was meant. This would only have visible consequences if the"__name__" attribute were present but the "__module__" attributewasn't, which apparently never happens; but someday it might.Rearranging the PG_TRY blocks requires indenting a fair amountof code one more tab stop, which I'll do separately for clarity.Author: Tom Lane <tgl@sss.pgh.pa.us>Discussion:https://postgr.es/m/2954090.1748723636@sss.pgh.pa.usBackpatch-through: 13
1 parente5a3c9d commitc6f7f11

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‎src/pl/plpython/plpy_elog.c

Lines changed: 55 additions & 50 deletions
Original file line numberDiff line numberDiff line change
@@ -18,7 +18,8 @@ PyObject *PLy_exc_spi_error = NULL;
1818

1919

2020
staticvoidPLy_traceback(PyObject*e,PyObject*v,PyObject*tb,
21-
char**xmsg,char**tbmsg,int*tb_depth);
21+
char*volatile*xmsg,char*volatile*tbmsg,
22+
int*tb_depth);
2223
staticvoidPLy_get_spi_error_data(PyObject*exc,int*sqlerrcode,char**detail,
2324
char**hint,char**query,int*position,
2425
char**schema_name,char**table_name,char**column_name,
@@ -43,13 +44,23 @@ void
4344
PLy_elog_impl(intelevel,constchar*fmt,...)
4445
{
4546
intsave_errno=errno;
46-
char*xmsg;
47-
char*tbmsg;
47+
char*volatilexmsg=NULL;
48+
char*volatiletbmsg=NULL;
4849
inttb_depth;
4950
StringInfoDataemsg;
5051
PyObject*exc,
5152
*val,
5253
*tb;
54+
55+
/* If we'll need emsg, must initialize it before entering PG_TRY */
56+
if (fmt)
57+
initStringInfo(&emsg);
58+
59+
PyErr_Fetch(&exc,&val,&tb);
60+
61+
/* Use a PG_TRY block to ensure we release the PyObjects just acquired */
62+
PG_TRY();
63+
{
5364
constchar*primary=NULL;
5465
intsqlerrcode=0;
5566
char*detail=NULL;
@@ -62,8 +73,6 @@ PLy_elog_impl(int elevel, const char *fmt,...)
6273
char*datatype_name=NULL;
6374
char*constraint_name=NULL;
6475

65-
PyErr_Fetch(&exc,&val,&tb);
66-
6776
if (exc!=NULL)
6877
{
6978
PyErr_NormalizeException(&exc,&val,&tb);
@@ -81,13 +90,11 @@ PLy_elog_impl(int elevel, const char *fmt,...)
8190
elevel=FATAL;
8291
}
8392

84-
/* this releases our refcount on tb! */
8593
PLy_traceback(exc,val,tb,
8694
&xmsg,&tbmsg,&tb_depth);
8795

8896
if (fmt)
8997
{
90-
initStringInfo(&emsg);
9198
for (;;)
9299
{
93100
va_listap;
@@ -113,8 +120,6 @@ PLy_elog_impl(int elevel, const char *fmt,...)
113120
primary=xmsg;
114121
}
115122

116-
PG_TRY();
117-
{
118123
ereport(elevel,
119124
(errcode(sqlerrcode ?sqlerrcode :ERRCODE_EXTERNAL_ROUTINE_EXCEPTION),
120125
errmsg_internal("%s",primary ?primary :"no exception data"),
@@ -136,14 +141,23 @@ PLy_elog_impl(int elevel, const char *fmt,...)
136141
}
137142
PG_FINALLY();
138143
{
144+
Py_XDECREF(exc);
145+
Py_XDECREF(val);
146+
/* Must release all the objects in the traceback stack */
147+
while (tb!=NULL&&tb!=Py_None)
148+
{
149+
PyObject*tb_prev=tb;
150+
151+
tb=PyObject_GetAttrString(tb,"tb_next");
152+
Py_DECREF(tb_prev);
153+
}
154+
/* For neatness' sake, also release our string buffers */
139155
if (fmt)
140156
pfree(emsg.data);
141157
if (xmsg)
142158
pfree(xmsg);
143159
if (tbmsg)
144160
pfree(tbmsg);
145-
Py_XDECREF(exc);
146-
Py_XDECREF(val);
147161
}
148162
PG_END_TRY();
149163
}
@@ -154,21 +168,14 @@ PLy_elog_impl(int elevel, const char *fmt,...)
154168
* The exception error message is returned in xmsg, the traceback in
155169
* tbmsg (both as palloc'd strings) and the traceback depth in
156170
* tb_depth.
157-
*
158-
* We release refcounts on all the Python objects in the traceback stack,
159-
* but not on e or v.
160171
*/
161172
staticvoid
162173
PLy_traceback(PyObject*e,PyObject*v,PyObject*tb,
163-
char**xmsg,char**tbmsg,int*tb_depth)
174+
char*volatile*xmsg,char*volatile*tbmsg,int*tb_depth)
164175
{
165-
PyObject*e_type_o;
166-
PyObject*e_module_o;
167-
char*e_type_s=NULL;
168-
char*e_module_s=NULL;
169-
PyObject*vob=NULL;
170-
char*vstr;
171-
StringInfoDataxstr;
176+
PyObject*volatilee_type_o=NULL;
177+
PyObject*volatilee_module_o=NULL;
178+
PyObject*volatilevob=NULL;
172179
StringInfoDatatbstr;
173180

174181
/*
@@ -186,12 +193,18 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
186193
/*
187194
* Format the exception and its value and put it in xmsg.
188195
*/
196+
PG_TRY();
197+
{
198+
char*e_type_s=NULL;
199+
char*e_module_s=NULL;
200+
constchar*vstr;
201+
StringInfoDataxstr;
189202

190203
e_type_o=PyObject_GetAttrString(e,"__name__");
191204
e_module_o=PyObject_GetAttrString(e,"__module__");
192205
if (e_type_o)
193206
e_type_s=PLyUnicode_AsString(e_type_o);
194-
if (e_type_s)
207+
if (e_module_o)
195208
e_module_s=PLyUnicode_AsString(e_module_o);
196209

197210
if (v&& ((vob=PyObject_Str(v))!=NULL))
@@ -215,18 +228,24 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
215228
appendStringInfo(&xstr,": %s",vstr);
216229

217230
*xmsg=xstr.data;
231+
}
232+
PG_FINALLY();
233+
{
234+
Py_XDECREF(e_type_o);
235+
Py_XDECREF(e_module_o);
236+
Py_XDECREF(vob);
237+
}
238+
PG_END_TRY();
218239

219240
/*
220241
* Now format the traceback and put it in tbmsg.
221242
*/
222-
223243
*tb_depth=0;
224244
initStringInfo(&tbstr);
225245
/* Mimic Python traceback reporting as close as possible. */
226246
appendStringInfoString(&tbstr,"Traceback (most recent call last):");
227247
while (tb!=NULL&&tb!=Py_None)
228248
{
229-
PyObject*volatiletb_prev=NULL;
230249
PyObject*volatileframe=NULL;
231250
PyObject*volatilecode=NULL;
232251
PyObject*volatilename=NULL;
@@ -254,17 +273,6 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
254273
filename=PyObject_GetAttrString(code,"co_filename");
255274
if (filename==NULL)
256275
elog(ERROR,"could not get file name from Python code object");
257-
}
258-
PG_CATCH();
259-
{
260-
Py_XDECREF(frame);
261-
Py_XDECREF(code);
262-
Py_XDECREF(name);
263-
Py_XDECREF(lineno);
264-
Py_XDECREF(filename);
265-
PG_RE_THROW();
266-
}
267-
PG_END_TRY();
268276

269277
/* The first frame always points at <module>, skip it. */
270278
if (*tb_depth>0)
@@ -320,29 +328,26 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
320328
}
321329
}
322330
}
331+
}
332+
PG_FINALLY();
333+
{
334+
Py_XDECREF(frame);
335+
Py_XDECREF(code);
336+
Py_XDECREF(name);
337+
Py_XDECREF(lineno);
338+
Py_XDECREF(filename);
339+
}
340+
PG_END_TRY();
323341

324-
Py_DECREF(frame);
325-
Py_DECREF(code);
326-
Py_DECREF(name);
327-
Py_DECREF(lineno);
328-
Py_DECREF(filename);
329-
330-
/* Release the current frame and go to the next one. */
331-
tb_prev=tb;
342+
/* Advance to the next frame. */
332343
tb=PyObject_GetAttrString(tb,"tb_next");
333-
Assert(tb_prev!=Py_None);
334-
Py_DECREF(tb_prev);
335344
if (tb==NULL)
336345
elog(ERROR,"could not traverse Python traceback");
337346
(*tb_depth)++;
338347
}
339348

340349
/* Return the traceback. */
341350
*tbmsg=tbstr.data;
342-
343-
Py_XDECREF(e_type_o);
344-
Py_XDECREF(e_module_o);
345-
Py_XDECREF(vob);
346351
}
347352

348353
/*

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