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

gpshead · web-flow · commit 746b2d35ea47 · 2018-11-13T13:16:54.000-08:00
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"'
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
@@ -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
@@ -6069,7 +6069,7 @@ _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 */

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+Fixed an out of bounds memory access when parsing a truncated unicode`
	`2`	+escape sequence at the end of a string such as ``'\N'``. It would read
	`3`	`+one byte beyond the end of the memory allocation.`
Original file line number	Diff line number	Diff line change
`@@ -6069,7 +6069,7 @@ _PyUnicode_DecodeUnicodeEscape(const char *s,`
`6069`	`6069`	`}`
`6070`	`6070`
`6071`	`6071`	`message = "malformed \\N character escape";`
`6072`		`- if (*s == '{') {`
	`6072`	`+ if (s < end && *s == '{') {`
`6073`	`6073`	`const char *start = ++s;`
`6074`	`6074`	`size_t namelen;`
`6075`	`6075`	`/* look for the closing brace */`