hur hur. fusexmp (userspace fs) + autofs + mount --rbind equals BLURP

[Luke Kenneth Casson Leighton <lkcl@lkcl.net>]

anybody scared of ugly usage of linux kernel modules should look away,
_right_ now :)

... that having been said, this is quite a problem for mount --rbind.

repro setup:

1) install fuse.
2) install autofs.
3) write an /etc/autofs.media with a mountpoint /media/floppy
4) mkdir /mnt/test and run fusexmp /mnt/test &
5) mkdir /home/yourhome/media and mount --rbind /media /home/yourhome/media
6) attempt to access /mnt/test/home/yourhome/media/floppy

... and watch the little bits of kernel segfaults go _flying_ by...

this is with 2.6.8[.1-selinux1].

some clues as to there-might-be-a-problem-with-rbind are that the
problem does _not_ occur if you access /home/yourhome/media/floppy,
and a second clue is that if there are any subdirectories in /media
prior to running autofs, with a bit of dickering about with the
order of the above repro setup it's possible to _see_ those subdirectories
_even_ though you've done a mount --rbind.

i think i saw this occur when i swapped stages 4) and 5) above.

l.

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