From 1ace027335c9ca0ae400958aded936d04505ec86 Mon Sep 17 00:00:00 2001
From: jvoisin
Date: Tue, 30 May 2023 20:46:14 +0200
Subject: Add a check for overlapping copies in strcpy

---
 include/string.h                    |  9 ++++++++-
 tests/Makefile                      |  2 ++
 tests/test_strcpy_overwrite_over.c  | 15 +++++++++++++++
 tests/test_strcpy_overwrite_under.c | 15 +++++++++++++++
 4 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 tests/test_strcpy_overwrite_over.c
 create mode 100644 tests/test_strcpy_overwrite_under.c

diff --git a/include/string.h b/include/string.h
index f08eb4c..8685bb7 100644
--- a/include/string.h
+++ b/include/string.h
@@ -107,8 +107,15 @@ _FORTIFY_FN(strcat) char *strcat(char *__d, const char *__s)
 
 _FORTIFY_FN(strcpy) char *strcpy(char *__d, const char *__s)
 {
-	size_t __b = __bos(__d, 0);
+	size_t __n = strlen(__s) + 1;
+
+	/* trap if pointers are overlapping but not if dst == src.
+	 * gcc seems to like to generate code that relies on dst == src */
+	if ((__d < __s && __d + __n > __s) ||
+	    (__s < __d && __s + __n > __d))
+		__builtin_trap();
 
+	size_t __b = __bos(__d, 0);
 	if (strlen(__s) + 1 > __b)
 		__builtin_trap();
 	return __orig_strcpy(__d, __s);
diff --git a/tests/Makefile b/tests/Makefile
index 9cca6f5..18f55fe 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -13,6 +13,8 @@ TARGETS=test_memcpy_static_write  \
 	test_memset_dynamic_write  \
 	test_strcpy_static_write   \
 	test_strcat_static_write   \
+	test_strcpy_overwrite_over \
+	test_strcpy_overwrite_under\
 
 .SILENT:
 
diff --git a/tests/test_strcpy_overwrite_over.c b/tests/test_strcpy_overwrite_over.c
new file mode 100644
index 0000000..924b346
--- /dev/null
+++ b/tests/test_strcpy_overwrite_over.c
@@ -0,0 +1,15 @@
+#include "common.h"
+
+#include <string.h>
+
+int main(int argc, char** argv) {
+  char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
+  puts(buffer);
+
+  CHK_FAIL_START
+  strcpy(buffer+1, buffer);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_strcpy_overwrite_under.c b/tests/test_strcpy_overwrite_under.c
new file mode 100644
index 0000000..2442470
--- /dev/null
+++ b/tests/test_strcpy_overwrite_under.c
@@ -0,0 +1,15 @@
+#include "common.h"
+
+#include <string.h>
+
+int main(int argc, char** argv) {
+  char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
+  puts(buffer);
+
+  CHK_FAIL_START
+  strcpy(buffer-1, buffer);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
-- 
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