xdiff: fix leak in hunk_consumer()

Spotted by ASAN.

Since PyList_Append() does not "steal" a reference, Py_DECREF() is always
required. Perhaps, this is the largest leak in this series.

mercurial/cext/bdiff.c

@@ -1,340 +1,339 b''
 /*
  bdiff.c - efficient binary diff extension for Mercurial
 
  Copyright 2005, 2006 Matt Mackall <[e-mail]>
 
  This software may be used and distributed according to the terms of
  the GNU General Public License, incorporated herein by reference.
 
  Based roughly on Python difflib
 */
 
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "bdiff.h"
 #include "bitmanipulation.h"
 #include "thirdparty/xdiff/xdiff.h"
 #include "util.h"
 
 static PyObject *blocks(PyObject *self, PyObject *args)
 {
 	PyObject *sa, *sb, *rl = NULL, *m;
 	struct bdiff_line *a, *b;
 	struct bdiff_hunk l, *h;
 	int an, bn, count, pos = 0;
 
 	l.next = NULL;
 
 	if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb))
 		return NULL;
 
 	an = bdiff_splitlines(PyBytes_AsString(sa), PyBytes_Size(sa), &a);
 	bn = bdiff_splitlines(PyBytes_AsString(sb), PyBytes_Size(sb), &b);
 
 	if (!a || !b)
 		goto nomem;
 
 	count = bdiff_diff(a, an, b, bn, &l);
 	if (count < 0)
 		goto nomem;
 
 	rl = PyList_New(count);
 	if (!rl)
 		goto nomem;
 
 	for (h = l.next; h; h = h->next) {
 		m = Py_BuildValue("iiii", h->a1, h->a2, h->b1, h->b2);
 		PyList_SetItem(rl, pos, m);
 		pos++;
 	}
 
 nomem:
 	free(a);
 	free(b);
 	bdiff_freehunks(l.next);
 	return rl ? rl : PyErr_NoMemory();
 }
 
 static PyObject *bdiff(PyObject *self, PyObject *args)
 {
 	Py_buffer ba, bb;
 	char *rb, *ia, *ib;
 	PyObject *result = NULL;
 	struct bdiff_line *al = NULL, *bl = NULL;
 	struct bdiff_hunk l, *h;
 	int an, bn, count;
 	Py_ssize_t len = 0, la, lb, li = 0, lcommon = 0, lmax;
 	PyThreadState *_save = NULL;
 
 	l.next = NULL;
 
 	if (!PyArg_ParseTuple(args, PY23("s*s*:bdiff", "y*y*:bdiff"), &ba, &bb))
 		return NULL;
 
 	if (!PyBuffer_IsContiguous(&ba, 'C') || ba.ndim > 1) {
 		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
 		goto cleanup;
 	}
 
 	if (!PyBuffer_IsContiguous(&bb, 'C') || bb.ndim > 1) {
 		PyErr_SetString(PyExc_ValueError, "bdiff input not contiguous");
 		goto cleanup;
 	}
 
 	la = ba.len;
 	lb = bb.len;
 
 	if (la > UINT_MAX || lb > UINT_MAX) {
 		PyErr_SetString(PyExc_ValueError, "bdiff inputs too large");
 		goto cleanup;
 	}
 
 	_save = PyEval_SaveThread();
 
 	lmax = la > lb ? lb : la;
 	for (ia = ba.buf, ib = bb.buf; li < lmax && *ia == *ib;
 	     ++li, ++ia, ++ib) {
 		if (*ia == '\n')
 			lcommon = li + 1;
 	}
 	/* we can almost add: if (li == lmax) lcommon = li; */
 
 	an = bdiff_splitlines((char *)ba.buf + lcommon, la - lcommon, &al);
 	bn = bdiff_splitlines((char *)bb.buf + lcommon, lb - lcommon, &bl);
 	if (!al || !bl) {
 		PyErr_NoMemory();
 		goto cleanup;
 	}
 
 	count = bdiff_diff(al, an, bl, bn, &l);
 	if (count < 0) {
 		PyErr_NoMemory();
 		goto cleanup;
 	}
 
 	/* calculate length of output */
 	la = lb = 0;
 	for (h = l.next; h; h = h->next) {
 		if (h->a1 != la || h->b1 != lb)
 			len += 12 + bl[h->b1].l - bl[lb].l;
 		la = h->a2;
 		lb = h->b2;
 	}
 	PyEval_RestoreThread(_save);
 	_save = NULL;
 
 	result = PyBytes_FromStringAndSize(NULL, len);
 
 	if (!result)
 		goto cleanup;
 
 	/* build binary patch */
 	rb = PyBytes_AsString(result);
 	la = lb = 0;
 
 	for (h = l.next; h; h = h->next) {
 		if (h->a1 != la || h->b1 != lb) {
 			len = bl[h->b1].l - bl[lb].l;
 			putbe32((uint32_t)(al[la].l + lcommon - al->l), rb);
 			putbe32((uint32_t)(al[h->a1].l + lcommon - al->l),
 			        rb + 4);
 			putbe32((uint32_t)len, rb + 8);
 			memcpy(rb + 12, bl[lb].l, len);
 			rb += 12 + len;
 		}
 		la = h->a2;
 		lb = h->b2;
 	}
 
 cleanup:
 	if (_save)
 		PyEval_RestoreThread(_save);
 	PyBuffer_Release(&ba);
 	PyBuffer_Release(&bb);
 	free(al);
 	free(bl);
 	bdiff_freehunks(l.next);
 	return result;
 }
 
 /*
  * If allws != 0, remove all whitespace (' ', \t and \r). Otherwise,
  * reduce whitespace sequences to a single space and trim remaining whitespace
  * from end of lines.
  */
 static PyObject *fixws(PyObject *self, PyObject *args)
 {
 	PyObject *s, *result = NULL;
 	char allws, c;
 	const char *r;
 	Py_ssize_t i, rlen, wlen = 0;
 	char *w;
 
 	if (!PyArg_ParseTuple(args, "Sb:fixws", &s, &allws))
 		return NULL;
 	r = PyBytes_AsString(s);
 	rlen = PyBytes_Size(s);
 
 	w = (char *)PyMem_Malloc(rlen ? rlen : 1);
 	if (!w)
 		goto nomem;
 
 	for (i = 0; i != rlen; i++) {
 		c = r[i];
 		if (c == ' ' || c == '\t' || c == '\r') {
 			if (!allws && (wlen == 0 || w[wlen - 1] != ' '))
 				w[wlen++] = ' ';
 		} else if (c == '\n' && !allws && wlen > 0 &&
 		           w[wlen - 1] == ' ') {
 			w[wlen - 1] = '\n';
 		} else {
 			w[wlen++] = c;
 		}
 	}
 
 	result = PyBytes_FromStringAndSize(w, wlen);
 
 nomem:
 	PyMem_Free(w);
 	return result ? result : PyErr_NoMemory();
 }
 
 static bool sliceintolist(PyObject *list, Py_ssize_t destidx,
                           const char *source, Py_ssize_t len)
 {
 	PyObject *sliced = PyBytes_FromStringAndSize(source, len);
 	if (sliced == NULL)
 		return false;
 	PyList_SET_ITEM(list, destidx, sliced);
 	return true;
 }
 
 static PyObject *splitnewlines(PyObject *self, PyObject *args)
 {
 	const char *text;
 	Py_ssize_t nelts = 0, size, i, start = 0;
 	PyObject *result = NULL;
 
 	if (!PyArg_ParseTuple(args, PY23("s#", "y#"), &text, &size)) {
 		goto abort;
 	}
 	if (!size) {
 		return PyList_New(0);
 	}
 	/* This loops to size-1 because if the last byte is a newline,
 	 * we don't want to perform a split there. */
 	for (i = 0; i < size - 1; ++i) {
 		if (text[i] == '\n') {
 			++nelts;
 		}
 	}
 	if ((result = PyList_New(nelts + 1)) == NULL)
 		goto abort;
 	nelts = 0;
 	for (i = 0; i < size - 1; ++i) {
 		if (text[i] == '\n') {
 			if (!sliceintolist(result, nelts++, text + start,
 			                   i - start + 1))
 				goto abort;
 			start = i + 1;
 		}
 	}
 	if (!sliceintolist(result, nelts++, text + start, size - start))
 		goto abort;
 	return result;
 abort:
 	Py_XDECREF(result);
 	return NULL;
 }
 
 static int hunk_consumer(int64_t a1, int64_t a2, int64_t b1, int64_t b2,
                          void *priv)
 {
 	PyObject *rl = (PyObject *)priv;
 	PyObject *m = Py_BuildValue("LLLL", a1, a2, b1, b2);
+	int r;
 	if (!m)
 		return -1;
-	if (PyList_Append(rl, m) != 0) {
-		Py_DECREF(m);
-		return -1;
-	}
-	return 0;
+	r = PyList_Append(rl, m);
+	Py_DECREF(m);
+	return r;
 }
 
 static PyObject *xdiffblocks(PyObject *self, PyObject *args)
 {
 	Py_ssize_t la, lb;
 	mmfile_t a, b;
 	PyObject *rl;
 
 	xpparam_t xpp = {
 	    XDF_INDENT_HEURISTIC, /* flags */
 	};
 	xdemitconf_t xecfg = {
 	    XDL_EMIT_BDIFFHUNK, /* flags */
 	    hunk_consumer,      /* hunk_consume_func */
 	};
 	xdemitcb_t ecb = {
 	    NULL, /* priv */
 	};
 
 	if (!PyArg_ParseTuple(args, PY23("s#s#", "y#y#"), &a.ptr, &la, &b.ptr,
 	                      &lb))
 		return NULL;
 
 	a.size = la;
 	b.size = lb;
 
 	rl = PyList_New(0);
 	if (!rl)
 		return PyErr_NoMemory();
 
 	ecb.priv = rl;
 
 	if (xdl_diff(&a, &b, &xpp, &xecfg, &ecb) != 0) {
 		Py_DECREF(rl);
 		return PyErr_NoMemory();
 	}
 
 	return rl;
 }
 
 static char mdiff_doc[] = "Efficient binary diff.";
 
 static PyMethodDef methods[] = {
     {"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"},
     {"blocks", blocks, METH_VARARGS, "find a list of matching lines\n"},
     {"fixws", fixws, METH_VARARGS, "normalize diff whitespaces\n"},
     {"splitnewlines", splitnewlines, METH_VARARGS,
      "like str.splitlines, but only split on newlines\n"},
     {"xdiffblocks", xdiffblocks, METH_VARARGS,
      "find a list of matching lines using xdiff algorithm\n"},
     {NULL, NULL},
 };
 
 static const int version = 3;
 
 #ifdef IS_PY3K
 static struct PyModuleDef bdiff_module = {
     PyModuleDef_HEAD_INIT, "bdiff", mdiff_doc, -1, methods,
 };
 
 PyMODINIT_FUNC PyInit_bdiff(void)
 {
 	PyObject *m;
 	m = PyModule_Create(&bdiff_module);
 	PyModule_AddIntConstant(m, "version", version);
 	return m;
 }
 #else
 PyMODINIT_FUNC initbdiff(void)
 {
 	PyObject *m;
 	m = Py_InitModule3("bdiff", methods, mdiff_doc);
 	PyModule_AddIntConstant(m, "version", version);
 }
 #endif