diff mercurial/cext/dirs.c @ 43494:5d40317d42b7

dirs: reject consecutive slashes in paths

We shouldn't ever see those, and the fuzzer go really excited that if
it gives us a 65k string with 55k slashes in it we use a lot of RAM.

This is a better fix than what I tried in D7105. It was suggested by
Yuya, and I verified it does in fact cause the fuzzer to not OOM.

This is a revision of D7234, but with the missing set of an error
added. I added a unit test of the dirs behavior because I needed to
reason more carefully about the failure modes around consecutive
slashes.

Differential Revision: https://phab.mercurial-scm.org/D7252

--- a/mercurial/cext/dirs.c	Tue Nov 05 22:56:12 2019 -0500
+++ b/mercurial/cext/dirs.c	Thu Oct 17 19:29:22 2019 -0400
@@ -66,6 +66,14 @@
 	while ((pos = _finddir(cpath, pos - 1)) != -1) {
 		PyObject *val;
 
+		/* Sniff for trailing slashes, a marker of an invalid input. */
+		if (pos > 0 && cpath[pos - 1] == '/') {
+			PyErr_SetString(
+			    PyExc_ValueError,
+			    "found invalid consecutive slashes in path");
+			goto bail;
+		}
+
 		key = PyBytes_FromStringAndSize(cpath, pos);
 		if (key == NULL)
 			goto bail;