From a2745278eb03d63f4df8da4367f27ec8cab7deb9 Mon Sep 17 00:00:00 2001
From: jvoisin
Date: Sat, 30 Sep 2023 00:15:26 +0200
Subject: Add `strlen`

---
 README.md                       |  1 +
 include/string.h                | 17 +++++++++++++++++
 tests/Makefile                  |  1 +
 tests/test_strlen_static_read.c | 22 ++++++++++++++++++++++
 4 files changed, 41 insertions(+)
 create mode 100644 tests/test_strlen_static_read.c

diff --git a/README.md b/README.md
index 9d4dacf..5ec6c5a 100644
--- a/README.md
+++ b/README.md
@@ -97,6 +97,7 @@ At this point, the program will safely crash.
 - `strcpy`
 - `strlcat`
 - `strlcpy`
+- `strlen`
 - `strncat`
 - `strncpy`
 - `strrchr`
diff --git a/include/string.h b/include/string.h
index e681181..ab7ac43 100644
--- a/include/string.h
+++ b/include/string.h
@@ -35,6 +35,7 @@ extern "C" {
 #undef memset
 #undef strcat
 #undef strcpy
+#undef strlen
 #undef strncat
 #undef strncpy
 
@@ -237,6 +238,22 @@ _FORTIFY_FN(strcpy) char *strcpy(char * _FORTIFY_POS0 __d, const char *__s)
 #endif
 }
 
+__access (read_only, 1)
+#if __has_builtin(__builtin_strlen)
+__diagnose_as_builtin(__builtin_strlen, 1)
+#endif
+_FORTIFY_FN(strlen) size_t strlen(const char * _FORTIFY_POS0 __s)
+{
+#if __has_builtin(__builtin___strlen_chk) && USE_NATIVE_CHK
+	return __builtin___strlen_chk(__s, __bos(__s, 0));
+#else
+	size_t ret = __orig_strlen(__s);
+	if (ret > __bos(__s, 0) - 1)
+		__builtin_trap();
+	return ret;
+#endif
+}
+
 __access (read_write, 1)
 __access (read_only, 2, 3)
 #if __has_builtin(__builtin_strncat)
diff --git a/tests/Makefile b/tests/Makefile
index 81593cf..c862c52 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -87,6 +87,7 @@ RUNTIME_TARGETS= \
 	test_stpncpy_overwrite_over  \
 	test_stpncpy_overwrite_under \
 	test_stpncpy_static_write    \
+	test_strlen_static_read      \
 	test_strcat_static_write     \
 	test_strchr_dynamic_read     \
 	test_strchr_static_read      \
diff --git a/tests/test_strlen_static_read.c b/tests/test_strlen_static_read.c
new file mode 100644
index 0000000..b1f928d
--- /dev/null
+++ b/tests/test_strlen_static_read.c
@@ -0,0 +1,22 @@
+#define _GNU_SOURCE
+#define _BSD_SOURCE
+
+#include "common.h"
+
+#include <string.h>
+
+int main(int argc, char** argv) {
+  char* canary1 = "ABCDEFGHIJKLMNOPQ";
+  char buf[] = {'a', 'b', 'c', 'd', '\0'};
+  char* canary2 = "ABCDEF";
+  strlen(buf);
+  puts(buf);
+  buf[4] = 'e';
+
+  CHK_FAIL_START
+  strlen(buf);
+  CHK_FAIL_END
+
+  puts(argv[1]);
+  return ret;
+}
-- 
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