1 files changed, 15 insertions, 1 deletions

diff --git a/include/stdio.h b/include/stdio.h
index 070d4e5..285fe21 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -6,17 +6,24 @@
 
 #if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0 && defined(__OPTIMIZE__) && __OPTIMIZE__ > 0
 
+#define __errordecl(name, msg) extern void name(void) __attribute__((__error__(msg)))
+
+__errordecl(__fgets_error, "fgets: buffer overflow detected");
 static inline __attribute__ ((always_inline))
 char *
 __fortify_fgets(char *s, int n, FILE *fp)
 {
         size_t bos = __builtin_object_size(s, 0);
 
+        if (__builtin_constant_p(n) && (size_t)n > bos)
+                __fgets_error();
+
         if ((size_t)n > bos)
                 __builtin_trap();
         return fgets(s, n, fp);
 }
 
+__errordecl(__vsnprintf_error, "vsnprintf: buffer overflow detected");
 static inline
 __attribute__ ((always_inline))
 __attribute__ ((__format__ (printf, 3, 0)))
@@ -27,6 +34,9 @@ __fortify_vsnprintf(char *__restrict s, size_t n, const char *__restrict fmt,
 {
         size_t bos = __builtin_object_size(s, 0);
 
+        if (__builtin_constant_p(n) && n > bos)
+                __vsnprintf_error();
+
         if (n > bos)
                 __builtin_trap();
         return vsnprintf(s, n, fmt, ap);
@@ -36,13 +46,17 @@ __fortify_vsnprintf(char *__restrict s, size_t n, const char *__restrict fmt,
 #define fgets(s, n, fp) __fortify_fgets(s, n, fp)
 #undef vsnprintf
 #define vsnprintf(s, n, fmt, ap) __fortify_vsnprintf(s, n, fmt, ap)
+
+__errordecl(__snprintf_error, "snprintf: buffer overflow detected");
 #undef snprintf
 #define snprintf(s, n, fmt, ...) ({ \
         size_t _n = (n); \
         size_t bos = __builtin_object_size(s, 0); \
+        if (__builtin_constant_p(_n) && _n > bos) \
+                __snprintf_error(); \
         if (_n > bos) \
                 __builtin_trap(); \
-        snprintf(s, _n, fmt, __VA_ARGS__); \
+        snprintf(s, _n, fmt, ## __VA_ARGS__); \
 })
 
 #endif