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Re: [bug] :P modifier and symlink loops
Stephane Chazelas wrote on Sun, 02 Feb 2020 17:03 +0000:
> 2020-02-02 08:10:21 +0000, Daniel Shahaf:
> [...]
> > However, in ${${:-"/tmp/loop/../foo"}} we can't meet the postcondition.
> > I think our options are either to throw an exception, like a glob with
> > no matches does, or to keep the additional components verbatim, as you
> > suggest.
> >
> > Intuitively I lean towards the first option. We aren't a CGI script,
> > where PATH_INFO is to be expected. If we can't return a path without
> > dot and dot-dot components and without symlinks, we should raise an
> > error rather than continue silently. However, I'm open to alternatives.
>
> That works for me, I agree it's a pathological condition that
> may be worth reporting to the user, and to do that, there's
> probably no other alternative than to exit the current shell
> process.
>
> > I think the first option could be implemented along the lines of:
> >
> > 1. Call realpath($arg).
> > 2. If it returns ELOOP,
>
> ... and doesn't end in /..
I assume you mean "ends in slash-dot-dot".
> the . path components would have to be removed first as well.
Good point, but I'd expect slightly different behaviour. Dot and
dot-dot components before the last, may-be-loop components don't need
special handling; they'll get resolved in the ordinary way. However,
if [[ $arg == (*/|*/.|*/..) ]], the ELOOP special case shouldn't be
applied.
The cases that $arg is "", ".", or ".." are not going to report ELOOP,
are they?
> > call realpath(${arg:h}) and append "/${arg:t}".
>
> And what if *that* realpath() fails with ELOOP? Do we carry on
> with $arg:h:h?
No; we'll call zerr() [which sets errflag] and bail out, just like the
NO_MATCH option does. Only the last path component (after the last slash,
or the entire string if it has no slashes) will be allowed to be a loop.
> > 3. Otherwise, throw an exception (i.e., set errflag).
> [...]
>
Cheers,
Daniel
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