prevent CNAME/PTR parsing from reading data past the response end

[musl] / src / stdio / fileno.c

diff --git a/src/stdio/fileno.c b/src/stdio/fileno.c
index ba7f939..0bd0e98 100644 (file)
--- a/src/stdio/fileno.c
+++ b/src/stdio/fileno.c
@@ -1,13 +1,16 @@
 #include "stdio_impl.h"
+#include <errno.h>
 
 int fileno(FILE *f)
 {
-       /* f->fd never changes, but the lock must be obtained and released
-        * anyway since this function cannot return while another thread
-        * holds the lock. */
        FLOCK(f);
+       int fd = f->fd;
        FUNLOCK(f);
-       return f->fd;
+       if (fd < 0) {
+               errno = EBADF;
+               return -1;
+       }
+       return fd;
 }
 
 weak_alias(fileno, fileno_unlocked);