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Fix edge-case resource leaks in PL/Python error reporting.

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PLy_elog_impl and its subroutine PLy_traceback intended to avoid
leaking any PyObject reference counts, but their coverage of the
matter was sadly incomplete.  In particular, out-of-memory errors
in most of the string-construction subroutines could lead to
reference count leaks, because those calls were outside the
PG_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 counts
of the traceback-stack objects to PLy_elog_impl.  This requires
some additional "volatile" markers, but not too many.

In passing, fix an ancient thinko: use of the "e_module_o" PyObject
was 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__" attribute
wasn't, which apparently never happens; but someday it might.

Rearranging the PG_TRY blocks requires indenting a fair amount
of 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.us
Backpatch-through: 13
This commit is contained in:
Tom Lane
2025-06-01 14:48:35 -04:00
parent ab52f6b5bf
commit 7559a16e23
1 changed files with 55 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files

105
src/pl/plpython/plpy_elog.c
View File

@ -18,7 +18,8 @@ PyObject *PLy_exc_spi_error = NULL;
static void PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
char **xmsg, char **tbmsg, int *tb_depth);
char *volatile *xmsg, char *volatile *tbmsg,
int *tb_depth);
static void PLy_get_spi_error_data(PyObject *exc, int *sqlerrcode, char **detail,
char **hint, char **query, int *position,
char **schema_name, char **table_name, char **column_name,
@ -43,13 +44,23 @@ void
PLy_elog_impl(int elevel, const char *fmt,...)
{
int save_errno = errno;
char *xmsg;
char *tbmsg;
char *volatile xmsg = NULL;
char *volatile tbmsg = NULL;
int tb_depth;
StringInfoData emsg;
PyObject *exc,
*val,
*tb;
/* If we'll need emsg, must initialize it before entering PG_TRY */
if (fmt)
initStringInfo(&emsg);
PyErr_Fetch(&exc, &val, &tb);
/* Use a PG_TRY block to ensure we release the PyObjects just acquired */
PG_TRY();
{
const char *primary = NULL;
int sqlerrcode = 0;
char *detail = NULL;
@ -62,8 +73,6 @@ PLy_elog_impl(int elevel, const char *fmt,...)
char *datatype_name = NULL;
char *constraint_name = NULL;
PyErr_Fetch(&exc, &val, &tb);
if (exc != NULL)
{
PyErr_NormalizeException(&exc, &val, &tb);
@ -81,13 +90,11 @@ PLy_elog_impl(int elevel, const char *fmt,...)
elevel = FATAL;
}
/* this releases our refcount on tb! */
PLy_traceback(exc, val, tb,
&xmsg, &tbmsg, &tb_depth);
if (fmt)
{
initStringInfo(&emsg);
for (;;)
{
va_list ap;
@ -113,8 +120,6 @@ PLy_elog_impl(int elevel, const char *fmt,...)
primary = xmsg;
}
PG_TRY();
{
ereport(elevel,
(errcode(sqlerrcode ? sqlerrcode : ERRCODE_EXTERNAL_ROUTINE_EXCEPTION),
errmsg_internal("%s", primary ? primary : "no exception data"),
@ -136,14 +141,23 @@ PLy_elog_impl(int elevel, const char *fmt,...)
}
PG_FINALLY();
{
Py_XDECREF(exc);
Py_XDECREF(val);
/* Must release all the objects in the traceback stack */
while (tb != NULL && tb != Py_None)
{
PyObject *tb_prev = tb;
tb = PyObject_GetAttrString(tb, "tb_next");
Py_DECREF(tb_prev);
}
/* For neatness' sake, also release our string buffers */
if (fmt)
pfree(emsg.data);
if (xmsg)
pfree(xmsg);
if (tbmsg)
pfree(tbmsg);
Py_XDECREF(exc);
Py_XDECREF(val);
}
PG_END_TRY();
}
@ -154,21 +168,14 @@ PLy_elog_impl(int elevel, const char *fmt,...)
* The exception error message is returned in xmsg, the traceback in
* tbmsg (both as palloc'd strings) and the traceback depth in
* tb_depth.
*
* We release refcounts on all the Python objects in the traceback stack,
* but not on e or v.
*/
static void
PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
char **xmsg, char **tbmsg, int *tb_depth)
char *volatile *xmsg, char *volatile *tbmsg, int *tb_depth)
{
PyObject *e_type_o;
PyObject *e_module_o;
char *e_type_s = NULL;
char *e_module_s = NULL;
PyObject *vob = NULL;
char *vstr;
StringInfoData xstr;
PyObject *volatile e_type_o = NULL;
PyObject *volatile e_module_o = NULL;
PyObject *volatile vob = NULL;
StringInfoData tbstr;
/*
@ -186,12 +193,18 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
/*
* Format the exception and its value and put it in xmsg.
*/
PG_TRY();
{
char *e_type_s = NULL;
char *e_module_s = NULL;
const char *vstr;
StringInfoData xstr;
e_type_o = PyObject_GetAttrString(e, "__name__");
e_module_o = PyObject_GetAttrString(e, "__module__");
if (e_type_o)
e_type_s = PLyUnicode_AsString(e_type_o);
if (e_type_s)
if (e_module_o)
e_module_s = PLyUnicode_AsString(e_module_o);
if (v && ((vob = PyObject_Str(v)) != NULL))
@ -215,18 +228,24 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
appendStringInfo(&xstr, ": %s", vstr);
*xmsg = xstr.data;
}
PG_FINALLY();
{
Py_XDECREF(e_type_o);
Py_XDECREF(e_module_o);
Py_XDECREF(vob);
}
PG_END_TRY();
/*
* Now format the traceback and put it in tbmsg.
*/
*tb_depth = 0;
initStringInfo(&tbstr);
/* Mimic Python traceback reporting as close as possible. */
appendStringInfoString(&tbstr, "Traceback (most recent call last):");
while (tb != NULL && tb != Py_None)
{
PyObject *volatile tb_prev = NULL;
PyObject *volatile frame = NULL;
PyObject *volatile code = NULL;
PyObject *volatile name = NULL;
@ -254,17 +273,6 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
filename = PyObject_GetAttrString(code, "co_filename");
if (filename == NULL)
elog(ERROR, "could not get file name from Python code object");
}
PG_CATCH();
{
Py_XDECREF(frame);
Py_XDECREF(code);
Py_XDECREF(name);
Py_XDECREF(lineno);
Py_XDECREF(filename);
PG_RE_THROW();
}
PG_END_TRY();
/* The first frame always points at <module>, skip it. */
if (*tb_depth > 0)
@ -320,18 +328,19 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
}
}
}
}
PG_FINALLY();
{
Py_XDECREF(frame);
Py_XDECREF(code);
Py_XDECREF(name);
Py_XDECREF(lineno);
Py_XDECREF(filename);
}
PG_END_TRY();
Py_DECREF(frame);
Py_DECREF(code);
Py_DECREF(name);
Py_DECREF(lineno);
Py_DECREF(filename);
/* Release the current frame and go to the next one. */
tb_prev = tb;
/* Advance to the next frame. */
tb = PyObject_GetAttrString(tb, "tb_next");
Assert(tb_prev != Py_None);
Py_DECREF(tb_prev);
if (tb == NULL)
elog(ERROR, "could not traverse Python traceback");
(*tb_depth)++;
@ -339,10 +348,6 @@ PLy_traceback(PyObject *e, PyObject *v, PyObject *tb,
/* Return the traceback. */
*tbmsg = tbstr.data;
Py_XDECREF(e_type_o);
Py_XDECREF(e_module_o);
Py_XDECREF(vob);
}
/*