libfuse accepts subtypes with slashes in them??

["Darrick J. Wong" <djwong@kernel.org>]

Hey everyone,

So today I noticed that this happens on Debian 13:

$ mount -t fuse./bin/ls /root/ /etc/shadow
ls: cannot access 'rw,dev,suid': No such file or directory
-rw-r----- 1 root 1345 Nov 18 10:38 /etc/shadow

ls: cannot open directory '/root': Permission denied

Uh... is that intentional?  It looks as though mount does:

execve("/sbin/mount.fuse", ["/sbin/mount.fuse", "/root", "/etc/shadow", "-o", "rw", "-t", "fuse./bin/ls"]...)

and then mount.fuse just trims off everything after the "fuse." and
does:

execve("/bin/sh", ["/bin/sh", "-c", "'/bin/ls' '/root' '/etc/shadow' '-o' 'rw,dev,suid'"]...)

with the odd output that you see above.  Is that supposed to happen?
Or should libfuse reject subtypes with path separators?

--D