dirs: resolve fuzzer OOM situation by disallowing deep directory hierarchies
authorAugie Fackler <augie@google.com>
Tue, 12 Nov 2019 10:17:59 -0500
changeset 43702 0796e266d26b
parent 43701 38387f9e4d22
child 43703 99e231afc29c
dirs: resolve fuzzer OOM situation by disallowing deep directory hierarchies It seems like 2048 directories ought to be enough for any reasonable use of Mercurial? A previous version of this patch scanned for slashes before any allocations occurred. That approach is slower than this in the happy path, but much faster than this in the case that too many slashes are encountered. We may want to revisit it in the future using memchr() so it'll be well-optimized by the libc we're using. .. bc: Mercurial will now defend against OOMs by refusing to operate on paths with 2048 or more components. This means that _extremely_ deep path hierarchies will be rejected, but we anticipate nobody is using hierarchies this deep. Differential Revision: https://phab.mercurial-scm.org/D7411
mercurial/cext/dirs.c
--- a/mercurial/cext/dirs.c	Thu Nov 14 14:14:11 2019 -0800
+++ b/mercurial/cext/dirs.c	Tue Nov 12 10:17:59 2019 -0500
@@ -9,6 +9,7 @@
 
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
+#include <string.h>
 
 #include "util.h"
 
@@ -48,12 +49,19 @@
 	return pos;
 }
 
+/* Mercurial will fail to run on directory hierarchies deeper than
+ * this constant, so we should try and keep this constant as big as
+ * possible.
+ */
+#define MAX_DIRS_DEPTH 2048
+
 static int _addpath(PyObject *dirs, PyObject *path)
 {
 	const char *cpath = PyBytes_AS_STRING(path);
 	Py_ssize_t pos = PyBytes_GET_SIZE(path);
 	PyObject *key = NULL;
 	int ret = -1;
+	size_t num_slashes = 0;
 
 	/* This loop is super critical for performance. That's why we inline
 	 * access to Python structs instead of going through a supported API.
@@ -65,6 +73,12 @@
 	 * unnoticed. */
 	while ((pos = _finddir(cpath, pos - 1)) != -1) {
 		PyObject *val;
+		++num_slashes;
+		if (num_slashes > MAX_DIRS_DEPTH) {
+			PyErr_SetString(PyExc_ValueError,
+			                "Directory hierarchy too deep.");
+			goto bail;
+		}
 
 		/* Sniff for trailing slashes, a marker of an invalid input. */
 		if (pos > 0 && cpath[pos - 1] == '/') {