unprivileged mount problems: device permissions ignored, mountsharing
From: utz lehmann
Date: Sun Apr 29 2007 - 15:00:54 EST
I tried the unprivileged mount v5 patches with 188.8.131.52. I made some
experiments with normal filesystems (ext3, xfs, iso9660). I removed the
FS_SAFE checks for that.
Mounting and umounting as unprivileged user (user1) works, e.g.
(/mnt/user1 is a mount owned by user1)
[user1@segv ~]$ mmount -t xfs /dev/mapper/vg00-test /mnt/user1
But the device permissions are ignored. The unprivileged user can mount
the block device even there are no permissions to access it:
brw------- 1 root root 253, 5 Apr 29 18:32 /dev/mapper/vg00-test
And there is another problem with sharing the device (superblock?).
If user1 mount a device readonly:
[user1@segv ~]$ mmount -r -t xfs /dev/mapper/vg00-test /mnt/user1
Than root cannot mount the device rw:
[root@segv ~]# mount /dev/mapper/vg00-test /mnt/test/
mount: /dev/mapper/vg00-test already mounted or /mnt/test/ busy
Mounting ro works and than remounting rw work. But than /mnt/user1 is rw
This can DoS e.g. the automounter mounting /dev/mapper/vg00-test rw.
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