Add tests for strncpy and handle overlapping buffers there

5 files changed, 70 insertions, 16 deletions

diff --git a/include/string.h b/include/string.h
index 9b6e601..f416a51 100644
--- a/include/string.h
+++ b/include/string.h
@@ -156,8 +156,13 @@ __access (write_only, 1)
 __access (read_only, 2, 3)
 _FORTIFY_FN(strncpy) char *strncpy(char *__d, const char *__s, size_t __n)
 {
-        size_t __b = __bos(__d, 0);
+        /* 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 (__n > __b)
                 __builtin_trap();
         return __orig_strncpy(__d, __s, __n);
diff --git a/tests/Makefile b/tests/Makefile
index 2c4e067..80a4626 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -2,21 +2,24 @@ CC=../x86_64-linux-musl-native/bin/gcc
 GCOV=../x86_64-linux-musl-native/bin/gcov
 CFLAGS=-I../include/ -D_FORTIFY_SOURCE=3 -static -O2
 
-TARGETS=test_memcpy_static_write  \
-        test_memcpy_dynamic_write  \
-        test_memcpy_static_read    \
-        test_memcpy_dynamic_read   \
-        test_memmove_static_write  \
-        test_memmove_dynamic_write \
-        test_memmove_static_read   \
-        test_memmove_dynamic_read  \
-        test_memset_static_write   \
-        test_memset_dynamic_write  \
-        test_strcpy_static_write   \
-        test_strcat_static_write   \
-        test_strcpy_overwrite_over \
-        test_strcpy_overwrite_under\
-        test_getcwd                \
+TARGETS=test_memcpy_static_write     \
+        test_memcpy_dynamic_write    \
+        test_memcpy_static_read      \
+        test_memcpy_dynamic_read     \
+        test_memmove_static_write    \
+        test_memmove_dynamic_write   \
+        test_memmove_static_read     \
+        test_memmove_dynamic_read    \
+        test_memset_static_write     \
+        test_memset_dynamic_write    \
+        test_strcpy_static_write     \
+        test_strcat_static_write     \
+        test_strcpy_overwrite_over   \
+        test_strcpy_overwrite_under  \
+        test_strncpy_static_write    \
+        test_strncpy_overwrite_over  \
+        test_strncpy_overwrite_under \
+        test_getcwd                  \
 
 .SILENT:
 
diff --git a/tests/test_strncpy_overwrite_over.c b/tests/test_strncpy_overwrite_over.c
new file mode 100644
index 0000000..d584bcc
--- /dev/null
+++ b/tests/test_strncpy_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
+  strncpy(buffer+1, buffer, 5);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_strncpy_overwrite_under.c b/tests/test_strncpy_overwrite_under.c
new file mode 100644
index 0000000..f554b28
--- /dev/null
+++ b/tests/test_strncpy_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
+  strncpy(buffer-1, buffer, 5);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}
diff --git a/tests/test_strncpy_static_write.c b/tests/test_strncpy_static_write.c
new file mode 100644
index 0000000..e619288
--- /dev/null
+++ b/tests/test_strncpy_static_write.c
@@ -0,0 +1,16 @@
+#include "common.h"
+
+#include <string.h>
+
+int main(int argc, char** argv) {
+  char buffer[8] = {0};
+  strncpy(buffer, "1234567", 5);
+  puts(buffer);
+
+  CHK_FAIL_START
+  strncpy(buffer, "1234567890", 10);
+  CHK_FAIL_END
+
+  puts(buffer);
+  return ret;
+}