tree 7ef2ed36a935d9643b6e6b50988054a603187755
parent 5c8fe583cce542aa0b84adc939ce85293de36e5e
author Al Viro <viro@zeniv.linux.org.uk> 1609791934 -0500
committer Al Viro <viro@zeniv.linux.org.uk> 1609792318 -0500

umount(2): move the flag validity checks first

Unfortunately, there's userland code that used to rely upon these
checks being done before anything else to check for UMOUNT_NOFOLLOW
support.  That broke in 41525f56e256 ("fs: refactor ksys_umount").
Separate those from the rest of checks and move them to ksys_umount();
unlike everything else in there, this can be sanely done there.

Reported-by: Sargun Dhillon <sargun@sargun.me>
Fixes: 41525f56e256 ("fs: refactor ksys_umount")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>