Add C11 error checking to vsnprintf()

C11 specifies that vsnprintf() is to check for the following conditions:
- output buffer or format string are null pointers
- buffer size is zero

C11 also specifies "constraint handler functions" that may be set, but that's far more involved, and having at least some error-handling for bad arguments like these is probably quite useful.

Source: https://en.cppreference.com/w/c/io/vfprintf#:~:text=5%2D8),constraint%20handler%20function%3A

1 files changed, 3 insertions, 0 deletions

diff --git a/libpsn00b/libc/vsprintf.c b/libpsn00b/libc/vsprintf.c
index 9ca4cc5..585d23d 100644
--- a/libpsn00b/libc/vsprintf.c
+++ b/libpsn00b/libc/vsprintf.c
@@ -391,6 +391,9 @@ int vsnprintf(char *string, unsigned int size, const char *fmt, va_list ap)
 	int zero_flag_imp = 0;
 	int pad_quantity = 0;
 	int last;
+
+	// C11: required to check these cases and return error if detected
+	if (string == NULL || fmt == NULL || size == 0) { return -1; }
 	
 	l = strlen(fmt);