The flag O_DIRECTORY can be used with the syscalls open(2) and openat(2) to avoid denial-of-service vulnerabilities when opening directories. However: How can I avoid the same kind of race conditions for regular files?
Some background information: I am trying to develop some kind of backup tool. The programs walks over a directory tree, reads all regular files and only stats other files. If I first call fstatat(2) for each directory entry, test the result for regular files and open them with openat(2), then there is a race condition between the syscalls. An attacker could replace the regular file with a FIFO, and my program would hang on the FIFO.
How can I avoid this race condition? For directories, there is O_DIRECTORY, for symbolic links, O_PATH can be used. However, I have found no solution for regular files. I only need a solution that works on recent Linux versions.