Re: [PATCH]: chmod - do inform about using different mode than requested with SGID/SUID/sticky bits without permissions to change them

[Ondřej Vašík]

Jim Meyering wrote:
> Ondřej Vašík <address@hidden> wrote:
> > as reported in
> > https://bugs.launchpad.net/ubuntu/+source/coreutils/+bug/187315 by Aaron
> > Toponce , chmod could display confusing messages when used for
> > SGID/SUID/sticky bits without permissions to change them.
> >
> > e.g. with non-root sudoers user following scenario
> > mkdir tmp;sudo chown .root tmp;ls -ld tmp;chmod -v 2755 tmp;ls -ld tmp;
> > would lead to:
> > drwxrwxr-x 2 Reset root 4096 24. říj 17.33 tmp
> > mode of `tmp' changed to 2755 (rwxr-sr-x)
> > drwxr-xr-x 2 Reset root 4096 24. říj 17.33 tmp
> >
> > So user is informed that sticky bit was set even if it was not.
> So, rather than trying to "fix" --changes, I'm leaning towards
> starting the process to remove it altogether.  From chmod,
> chown, and chgrp.
> 
> This may seem extreme, until you realize that the option is inherently
> inaccurate in some cases.  And the only way it can be accurate is if
> "<PROG> --changes ..." were to stat each file after operating on it.
> Of course, I wouldn't do that "for real".  We'd have to first
> deprecate the targeted options, making any use provoke a warning,
> and then -- years later -- un-document and finally, remove them.
> And I probably wouldn't even deprecate --verbose.
> 
> What do you think?

Throwing out "--changes" should be ok, if user wants to be informed, he
can parse verbose output easily and common case is to use it without
verbose mode at all. Anyway --verbose output is affected by this "issue"
as well, so I would prefer to 
1) depricate --changes option as it could be substituted by --verbose
and grep
2) fix the verbose output to show correct output in every case where it
is possible. E.g. if the stat fails, it should inform the user that the
mode/owner/whatever is unknown. E.g. SGID bit case or stat failed is the
thing where user should be informed in verbose mode about something
unusual.

Greetings,
         Ondrej

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