Fix segfaults when parsing bdiff hunks in mpatch.decode() and .patchedsize()

- fix off by 11 when checking if there are more hunks (found by Maris Fogels)
- bail out if start is greater than end
- check if new hunk starts after start/end/len block of current hunk as
  the pointer can wrap around on very large values, reproducible with
  import mpatch; mpatch.patchedsize(12, 'x'*12)

mercurial/mpatch.c

@@ -1,411 +1,422 b''
 /*
  mpatch.c - efficient binary patching for Mercurial
 
  This implements a patch algorithm that's O(m + nlog n) where m is the
  size of the output and n is the number of patches.
 
  Given a list of binary patches, it unpacks each into a hunk list,
  then combines the hunk lists with a treewise recursion to form a
  single hunk list. This hunk list is then applied to the original
  text.
 
  The text (or binary) fragments are copied directly from their source
  Python objects into a preallocated output string to avoid the
  allocation of intermediate Python objects. Working memory is about 2x
  the total number of hunks.
 
  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.
 */
 
 #include <Python.h>
 #include <stdlib.h>
 #include <string.h>
 
 #ifdef _WIN32
 # ifdef _MSC_VER
 /* msvc 6.0 has problems */
 #  define inline __inline
 typedef unsigned long uint32_t;
 # else
 #  include <stdint.h>
 # endif
 static uint32_t ntohl(uint32_t x)
 {
 	return ((x & 0x000000ffUL) << 24) |
 		((x & 0x0000ff00UL) <<  8) |
 		((x & 0x00ff0000UL) >>  8) |
 		((x & 0xff000000UL) >> 24);
 }
 #else
 /* not windows */
 # include <sys/types.h>
 # include <arpa/inet.h>
 # include <inttypes.h>
 #endif
 
 static char mpatch_doc[] = "Efficient binary patching.";
 static PyObject *mpatch_Error;
 
 struct frag {
 	int start, end, len;
 	char *data;
 };
 
 struct flist {
 	struct frag *base, *head, *tail;
 };
 
 static struct flist *lalloc(int size)
 {
 	struct flist *a = NULL;
 
 	if (size < 1)
 		size = 1;
 
 	a = (struct flist *)malloc(sizeof(struct flist));
 	if (a) {
 		a->base = (struct frag *)malloc(sizeof(struct frag) * size);
 		if (a->base) {
 			a->head = a->tail = a->base;
 			return a;
 		}
 		free(a);
 		a = NULL;
 	}
 	if (!PyErr_Occurred())
 		PyErr_NoMemory();
 	return NULL;
 }
 
 static void lfree(struct flist *a)
 {
 	if (a) {
 		free(a->base);
 		free(a);
 	}
 }
 
 static int lsize(struct flist *a)
 {
 	return a->tail - a->head;
 }
 
 /* move hunks in source that are less cut to dest, compensating
    for changes in offset. the last hunk may be split if necessary.
 */
 static int gather(struct flist *dest, struct flist *src, int cut, int offset)
 {
 	struct frag *d = dest->tail, *s = src->head;
 	int postend, c, l;
 
 	while (s != src->tail) {
 		if (s->start + offset >= cut)
 			break; /* we've gone far enough */
 
 		postend = offset + s->start + s->len;
 		if (postend <= cut) {
 			/* save this hunk */
 			offset += s->start + s->len - s->end;
 			*d++ = *s++;
 		}
 		else {
 			/* break up this hunk */
 			c = cut - offset;
 			if (s->end < c)
 				c = s->end;
 			l = cut - offset - s->start;
 			if (s->len < l)
 				l = s->len;
 
 			offset += s->start + l - c;
 
 			d->start = s->start;
 			d->end = c;
 			d->len = l;
 			d->data = s->data;
 			d++;
 			s->start = c;
 			s->len = s->len - l;
 			s->data = s->data + l;
 
 			break;
 		}
 	}
 
 	dest->tail = d;
 	src->head = s;
 	return offset;
 }
 
 /* like gather, but with no output list */
 static int discard(struct flist *src, int cut, int offset)
 {
 	struct frag *s = src->head;
 	int postend, c, l;
 
 	while (s != src->tail) {
 		if (s->start + offset >= cut)
 			break;
 
 		postend = offset + s->start + s->len;
 		if (postend <= cut) {
 			offset += s->start + s->len - s->end;
 			s++;
 		}
 		else {
 			c = cut - offset;
 			if (s->end < c)
 				c = s->end;
 			l = cut - offset - s->start;
 			if (s->len < l)
 				l = s->len;
 
 			offset += s->start + l - c;
 			s->start = c;
 			s->len = s->len - l;
 			s->data = s->data + l;
 
 			break;
 		}
 	}
 
 	src->head = s;
 	return offset;
 }
 
 /* combine hunk lists a and b, while adjusting b for offset changes in a/
    this deletes a and b and returns the resultant list. */
 static struct flist *combine(struct flist *a, struct flist *b)
 {
 	struct flist *c = NULL;
 	struct frag *bh, *ct;
 	int offset = 0, post;
 
 	if (a && b)
 		c = lalloc((lsize(a) + lsize(b)) * 2);
 
 	if (c) {
 
 		for (bh = b->head; bh != b->tail; bh++) {
 			/* save old hunks */
 			offset = gather(c, a, bh->start, offset);
 
 			/* discard replaced hunks */
 			post = discard(a, bh->end, offset);
 
 			/* insert new hunk */
 			ct = c->tail;
 			ct->start = bh->start - offset;
 			ct->end = bh->end - post;
 			ct->len = bh->len;
 			ct->data = bh->data;
 			c->tail++;
 			offset = post;
 		}
 
 		/* hold on to tail from a */
 		memcpy(c->tail, a->head, sizeof(struct frag) * lsize(a));
 		c->tail += lsize(a);
 	}
 
 	lfree(a);
 	lfree(b);
 	return c;
 }
 
 /* decode a binary patch into a hunk list */
 static struct flist *decode(char *bin, int len)
 {
 	struct flist *l;
 	struct frag *lt;
-	char *end = bin + len;
+	char *data = bin + 12, *end = bin + len;
 	char decode[12]; /* for dealing with alignment issues */
 
 	/* assume worst case size, we won't have many of these lists */
 	l = lalloc(len / 12);
 	if (!l)
 		return NULL;
 
 	lt = l->tail;
 
-	while (bin < end) {
+	while (data <= end) {
 		memcpy(decode, bin, 12);
 		lt->start = ntohl(*(uint32_t *)decode);
 		lt->end = ntohl(*(uint32_t *)(decode + 4));
 		lt->len = ntohl(*(uint32_t *)(decode + 8));
-		lt->data = bin + 12;
-		bin += 12 + lt->len;
+		if (lt->start > lt->end)
+			break; /* sanity check */
+		bin = data + lt->len;
+		if (bin < data)
+			break; /* big data + big (bogus) len can wrap around */
+		lt->data = data;
+		data = bin + 12;
 		lt++;
 	}
 
 	if (bin != end) {
 		if (!PyErr_Occurred())
 			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
 		lfree(l);
 		return NULL;
 	}
 
 	l->tail = lt;
 	return l;
 }
 
 /* calculate the size of resultant text */
 static int calcsize(int len, struct flist *l)
 {
 	int outlen = 0, last = 0;
 	struct frag *f = l->head;
 
 	while (f != l->tail) {
 		if (f->start < last || f->end > len) {
 			if (!PyErr_Occurred())
 				PyErr_SetString(mpatch_Error,
 				                "invalid patch");
 			return -1;
 		}
 		outlen += f->start - last;
 		last = f->end;
 		outlen += f->len;
 		f++;
 	}
 
 	outlen += len - last;
 	return outlen;
 }
 
 static int apply(char *buf, char *orig, int len, struct flist *l)
 {
 	struct frag *f = l->head;
 	int last = 0;
 	char *p = buf;
 
 	while (f != l->tail) {
 		if (f->start < last || f->end > len) {
 			if (!PyErr_Occurred())
 				PyErr_SetString(mpatch_Error,
 				                "invalid patch");
 			return 0;
 		}
 		memcpy(p, orig + last, f->start - last);
 		p += f->start - last;
 		memcpy(p, f->data, f->len);
 		last = f->end;
 		p += f->len;
 		f++;
 	}
 	memcpy(p, orig + last, len - last);
 	return 1;
 }
 
 /* recursively generate a patch of all bins between start and end */
 static struct flist *fold(PyObject *bins, int start, int end)
 {
 	int len;
 
 	if (start + 1 == end) {
 		/* trivial case, output a decoded list */
 		PyObject *tmp = PyList_GetItem(bins, start);
 		if (!tmp)
 			return NULL;
 		return decode(PyString_AsString(tmp), PyString_Size(tmp));
 	}
 
 	/* divide and conquer, memory management is elsewhere */
 	len = (end - start) / 2;
 	return combine(fold(bins, start, start + len),
 		       fold(bins, start + len, end));
 }
 
 static PyObject *
 patches(PyObject *self, PyObject *args)
 {
 	PyObject *text, *bins, *result;
 	struct flist *patch;
 	char *in, *out;
 	int len, outlen;
 
 	if (!PyArg_ParseTuple(args, "SO:mpatch", &text, &bins))
 		return NULL;
 
 	len = PyList_Size(bins);
 	if (!len) {
 		/* nothing to do */
 		Py_INCREF(text);
 		return text;
 	}
 
 	patch = fold(bins, 0, len);
 	if (!patch)
 		return NULL;
 
 	outlen = calcsize(PyString_Size(text), patch);
 	if (outlen < 0) {
 		result = NULL;
 		goto cleanup;
 	}
 	result = PyString_FromStringAndSize(NULL, outlen);
 	if (!result) {
 		result = NULL;
 		goto cleanup;
 	}
 	in = PyString_AsString(text);
 	out = PyString_AsString(result);
 	if (!apply(out, in, PyString_Size(text), patch)) {
 		Py_DECREF(result);
 		result = NULL;
 	}
 cleanup:
 	lfree(patch);
 	return result;
 }
 
 /* calculate size of a patched file directly */
 static PyObject *
 patchedsize(PyObject *self, PyObject *args)
 {
 	long orig, start, end, len, outlen = 0, last = 0;
 	int patchlen;
-	char *bin, *binend;
+	char *bin, *binend, *data;
 	char decode[12]; /* for dealing with alignment issues */
 
 	if (!PyArg_ParseTuple(args, "ls#", &orig, &bin, &patchlen))
 		return NULL;
 
 	binend = bin + patchlen;
+	data = bin + 12;
 
-	while (bin < binend) {
+	while (data <= binend) {
 		memcpy(decode, bin, 12);
 		start = ntohl(*(uint32_t *)decode);
 		end = ntohl(*(uint32_t *)(decode + 4));
 		len = ntohl(*(uint32_t *)(decode + 8));
-		bin += 12 + len;
+		if (start > end)
+			break; /* sanity check */
+		bin = data + len;
+		if (bin < data)
+			break; /* big data + big (bogus) len can wrap around */
+		data = bin + 12;
 		outlen += start - last;
 		last = end;
 		outlen += len;
 	}
 
 	if (bin != binend) {
 		if (!PyErr_Occurred())
 			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
 		return NULL;
 	}
 
 	outlen += orig - last;
 	return Py_BuildValue("l", outlen);
 }
 
 static PyMethodDef methods[] = {
 	{"patches", patches, METH_VARARGS, "apply a series of patches\n"},
 	{"patchedsize", patchedsize, METH_VARARGS, "calculed patched size\n"},
 	{NULL, NULL}
 };
 
 PyMODINIT_FUNC
 initmpatch(void)
 {
 	Py_InitModule3("mpatch", methods, mpatch_doc);
 	mpatch_Error = PyErr_NewException("mpatch.mpatchError", NULL, NULL);
 }