Added disable_symlinks directive. To completely disable symlinks (disable_symlinks on) we use openat(O_NOFOLLOW) for each path component to avoid races. To allow symlinks with the same owner (disable_symlinks if_not_owner), use openat() (followed by fstat()) and fstatat(AT_SYMLINK_NOFOLLOW), and then compare uids between fstat() and fstatat(). As there is a race between openat() and fstatat() we don't know if openat() in fact opened symlink or not. Therefore, we have to compare uids even if fstatat() reports the opened component isn't a symlink (as we don't know whether it was symlink during openat() or not). Default value is off, i.e. symlinks are allowed.

--- a/src/core/ngx_core.h
+++ b/src/core/ngx_core.h
@@ -91,5 +91,10 @@ typedef void (*ngx_connection_handler_pt
 
 void ngx_cpuinfo(void);
 
+#if (NGX_HAVE_OPENAT)
+#define NGX_DISABLE_SYMLINKS_OFF        0
+#define NGX_DISABLE_SYMLINKS_ON         1
+#define NGX_DISABLE_SYMLINKS_NOTOWNER   2
+#endif
 
 #endif /* _NGX_CORE_H_INCLUDED_ */