Messages in this thread | | | Subject | Re: [PATCHv2 1/5] VFS: DazukoFS, stackable-fs, file access control | From | John Ogness <> | Date | Fri, 13 Feb 2009 20:31:03 +0100 |
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On 2009-02-12, Jan Engelhardt <jengelh@medozas.de> wrote: >>+DazukoFS is typically mounted on top of an existing directory. For example, >>+to stack DazukoFS on top of the /opt directory, the following mount(8) >>+command can be given: >>+ >>+# mount -t dazukofs /opt /opt > [...] >>+# mount -t dazukofs /opt /mnt >>+ >>+When accessing files within /mnt, you will be accessing files in /opt >>+(through DazukoFS). When accessing files directly in /opt, DazukoFS will not >>+be involved. >>+ >>+THIS HAS POTENTIAL PROBLEMS! > > This ought to be done better in light of the problem that one > could issue `mount -t dazukofs /mnt /opt` > In kernel code, I'm thinking something like > > static int foofs_dothis(...) > { > buf = call d_path on sb->s_root > call namei_lookup on buf > use lookup's resulting dentry as source directory > } > > This assumes at least that namei_lookup will not return the new SB's > dentry for the given path. > Iff that works out somehow, the 'device' part in the mount command > line is practically ignored like it is for like procfs.
If we want to forbid users from being able to do this, I think it would be simpler just to fail the mount if it is _not_ specified for direct stacking. This forces users to use a syntax that makes it very clear what they are doing.
Since mounting to a different directory could cause problems, I think it will be good to forbid it. I will make this change for the next patch series.
John Ogness
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