bpo-35214: Fix OOB memory access in unicode escape parser (GH-10506)

Discovered using clang's MemorySanitizer when it ran python3's
test_fstring test_misformed_unicode_character_name.

An msan build will fail by simply executing: ./python -c 'u"\N"'
(cherry picked from commit 746b2d35ea47005054ed774fecaed64fab803d7d)

Co-authored-by: Gregory P. Smith <greg@krypto.org>

diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-11-13-00-40-35.bpo-35214.OQBjph.rst b/Misc/NEWS.d/next/Core and Builtins/2018-11-13-00-40-35.bpo-35214.OQBjph.rst
new file mode 100644 (file)
index 0000000..d462c97
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-11-13-00-40-35.bpo-35214.OQBjph.rst
@@ -0,0 +1,3 @@
+Fixed an out of bounds memory access when parsing a truncated unicode
+escape sequence at the end of a string such as ``'\N'``.  It would read
+one byte beyond the end of the memory allocation.

diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 972423e78da8c41d13e6be988abede495e29c3a7..1f342bd199c788874aa9cda485683e090f77be3a 100644 (file)
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -6133,7 +6133,7 @@ _PyUnicode_DecodeUnicodeEscape(const char *s,
             }
 
             message = "malformed \\N character escape";
-            if (*s == '{') {
+            if (s < end && *s == '{') {
                 const char *start = ++s;
                 size_t namelen;
                 /* look for the closing brace */