badly authored udf file systems

badly authored udf file systems

[Shaya Potter]

I have a couple of DVDs that seem to have been authored badly, such that
when they are mounted, none of the directories have the execute bit, and
hence means that only root can enter the VIDEO_TS folder and hence only
root can play the dvd.

in looking at the ecma spec
(http://www.ecma-international.org/publications/standards/Ecma-167.htm)
and section 4/14.9 where the file entry record is discussed, it shows
that the permission scheme sort of mirrors unix (i.e. owner, group,
other and read/write/execute bits).  However, the spec is ambigious
because when it refers to the execute bit, it doesn't talk about
directories at all.  In normal unix, of course one needs the execute bit
set, however, its probable other systems dont have such a semantic and
hence buggy dvd authoring programs on those platforms don't check for
it.

Would it be useful to have a file system option to specify something
along the lines "buggy_dvd" which automatically gives all directories a
0x111 bump?

I ran into this w/ gnome's gnome-volume-manager which automatically
mounted the dvd on insertion, but wasn't able to play it unless the dvd
player was running as root.

thanks,

shaya

Re: badly authored udf file systems

[Jamie Lokier]

Shaya Potter wrote:
> in looking at the ecma spec
> (http://www.ecma-international.org/publications/standards/Ecma-167.htm)
> and section 4/14.9 where the file entry record is discussed, it shows
> that the permission scheme sort of mirrors unix (i.e. owner, group,
> other and read/write/execute bits).  However, the spec is ambigious
> because when it refers to the execute bit, it doesn't talk about
> directories at all.  In normal unix, of course one needs the execute bit
> set, however, its probable other systems dont have such a semantic and
> hence buggy dvd authoring programs on those platforms don't check for
> it.
>
> Would it be useful to have a file system option to specify something
> along the lines "buggy_dvd" which automatically gives all directories a
> 0x111 bump?

If the spec doesn't talk about directory execute permissions at all,
and it looks like that is intended, then shouldn't the 0x111 bump be
done all the time for UDF?  More exactly, adding execute permissions
corresponding to whichever read permissions are set.

-- Jamie

Re: badly authored udf file systems

[Shaya Potter]

On Thu, 2004-12-02 at 10:03 +0000, Jamie Lokier wrote:
> Shaya Potter wrote:
> > in looking at the ecma spec
> > (http://www.ecma-international.org/publications/standards/Ecma-167.htm)
> > and section 4/14.9 where the file entry record is discussed, it shows
> > that the permission scheme sort of mirrors unix (i.e. owner, group,
> > other and read/write/execute bits).  However, the spec is ambigious
> > because when it refers to the execute bit, it doesn't talk about
> > directories at all.  In normal unix, of course one needs the execute bit
> > set, however, its probable other systems dont have such a semantic and
> > hence buggy dvd authoring programs on those platforms don't check for
> > it.
> >
> > Would it be useful to have a file system option to specify something
> > along the lines "buggy_dvd" which automatically gives all directories a
> > 0x111 bump?
> 
> If the spec doesn't talk about directory execute permissions at all,
> and it looks like that is intended, then shouldn't the 0x111 bump be
> done all the time for UDF?  More exactly, adding execute permissions
> corresponding to whichever read permissions are set.

perhaps, I didn't read through the entire spec, so don't know if
directory permissions are covered elsewhere (though a search of the pdf
for "directory permission" didn't find anything), just the part talking
about permissions.

specifically
---
14.9.5 Permissions (BP 44)
This field shall specify the access allowed to the current file for
certain classes of users as follows:
- If the user's user ID is the same as the Uid field, then bits 10-14
shall apply.
- Otherwise, if the user's group ID is the same as the Gid field, then
bits 5-9 shall apply.
- Otherwise, bits 0-4 shall apply.

Bit 0  = Other: If set to ZERO, shall mean that the user may not execute
the file; If set to ONE, shall mean that

....

Bit 5  = Group: If set to ZERO, shall mean that the user may not execute
the file; If set to ONE, shall mean that the user may execute the file.

....

Bit 10 = Owner: If set to ZERO, shall mean that the user may not execute
the file; If set to ONE, shall mean that the user may execute the file.
---

with the following note

---
Note 27
File access schemes are subject to agreement between the originator and
recipient of the medium as the meanings of both user IDs and group IDs
are implementation dependent; indeed, the permission and file access
models of the receiving and originating systems may be incompatible.

The question of how to interpret permissions on systems which do not
support user IDs and group IDs is outside the scope of Part 4. However,
if a system uses the Uid, Gid and Permissions fields, it is recommended
that such systems use and set all three (owner, group, other) sets of
permissions. It is also recommended that the Uid, Gid and Permissions
fields be mapped to the appropriate fields in the implementation.
---