The trouble with symbolic links

With all uncertainty, the approach that I mentioned, is to first hold file descriptor to something
that is nearest of the goal operation.
File descriptor is stable (Kernel guarantees that), so holding it prevents many kinds of race conditions.
Then validate the opened file descriptor based on trusted sources for security reasons.

After gaining trust for a folder file descriptor, use it in safe ways (for example create a file with symbolic links turned off).

So from Samba developer, /proc/self approach works for solving the real path for validation:

fd = openat(-1, "/bin", O_DIRECTORY); /* fd = 3 */
resolved_path = realpath("/proc/self/fd/3", NULL); /* resolved_path="/usr/bin" */

"/usr/bin" is safe, so fd 3 can be used for following operations.