Fix fopen/stdin issues with fuzzing

* fuzz/wget_options_fuzzer.c: Add fopen_wget() and fopen_wgetrc()
* src/utils.c: Use fopen_wgetrc() for config files,
  don't read from stdin when fuzzing
* src/wget.h: Define fopen as fopen_wget when fuzzing,
  define fopen_wgetrc as fopen when not fuzzing

fuzz/wget_options_fuzzer.c

@@ -80,6 +80,7 @@ DIR *opendir(const char *name)
 */
 }
 
+/*
 FILE *fopen(const char *pathname, const char *mode)
 {
 	FILE *(*libc_fopen)(const char *, const char *) =
@@ -105,6 +106,7 @@ FILE *fopen(const char *pathname, const char *mode)
 
 	return libc_fopen(pathname, mode);
 }
+*/
 
 void exit(int status)
 {
@@ -119,6 +121,16 @@ void exit(int status)
 #endif
 #endif
 
+FILE *fopen_wget(const char *pathname, const char *mode)
+{
+	return fopen("/dev/null", mode);
+}
+
+FILE *fopen_wgetrc(const char *pathname, const char *mode)
+{
+	return fmemopen((void *) g_data, g_size, mode);
+}
+
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
 //	static const char *argv[] = { "wget", "-q", "--no-config", "--config", "d41d8cd98f00b204e9800998ecf8427e" };

src/utils.c

@@ -848,9 +848,11 @@ fopen_stat(const char *fname, const char *mode, file_stats_t *fstats)
   FILE *fp;
   struct stat fdstats;
 
-  fp = fopen (fname, mode);
-#ifdef TESTING
+#if defined FUZZING && defined TESTING
+  fp = fopen_wgetrc (fname, mode);
   return fp;
+#else
+  fp = fopen (fname, mode);
 #endif
   if (fp == NULL)
   {
@@ -1277,6 +1279,7 @@ wget_read_file (const char *file)
 
   /* Some magic in the finest tradition of Perl and its kin: if FILE
      is "-", just use stdin.  */
+#ifndef FUZZING
   if (HYPHENP (file))
     {
       fd = fileno (stdin);
@@ -1285,6 +1288,7 @@ wget_read_file (const char *file)
          redirected from a regular file, mmap() will still work.  */
     }
   else
+#endif
     fd = open (file, O_RDONLY);
   if (fd < 0)
     return NULL;

src/wget.h

@@ -393,4 +393,18 @@ typedef enum
 #  define UNIQ_SEP '.'
 # endif /* ndef __VMS */
 
+#if defined FUZZING && defined TESTING
+/* Rename fopen so we can have our own version in fuzz/main.c to
+   not create random files. */
+#  define fopen(fp, mode) fopen_wget(fp, mode)
+
+/* In run_wgetrc() we call fopen_wgetrc() instead of fopen, so we can catch
+   the call in our fuzzers. */
+FILE *fopen_wget(const char *pathname, const char *mode);
+FILE *fopen_wgetrc(const char *pathname, const char *mode);
+#else
+/* When not fuzzing, we want to call fopen() instead of fopen_wgetrc() */
+#  define fopen_wgetrc(fp) fopen(fp)
+#endif /* FUZZING && TESTING */
+
 #endif /* WGET_H */