Re: Dangerous commands (was:[ANNOUNCE] fstests: for-next branch updated to v2024.02.04)

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Feb 26, 2024 at 10:56:29AM +0800, Zorro Lang wrote:
> On Sun, Feb 25, 2024 at 09:45:27AM -0800, Eric Biggers wrote:
> > On Sun, Feb 25, 2024 at 09:03:04AM -0800, Darrick J. Wong wrote:
> > > On Sun, Feb 25, 2024 at 08:51:28AM -0800, Eric Biggers wrote:
> > > > On Sun, Feb 25, 2024 at 11:16:16PM +0800, Zorro Lang wrote:
> > > > > On Wed, Feb 21, 2024 at 03:09:51PM +0100, David Sterba wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > reading [1] and how late it was found that effectively a "rm -rf /" can
> > > > > > happen makes me worried about what I can expect from fstests after git
> > > > > > pull. Many people contribute and the number for custom _cleanup()
> > > > > > functions with unquoted 'rm' commands is just asking for more problems.
> > > > > > 
> > > > > > [1] https://lore.kernel.org/all/20240205060016.7fgiyafbnrvf5chj@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com/
> > > > > > 
> > > > > > Unquoted arguments in shell scripts is IMO a big anti-pattern,
> > > > > > unfortunately present everywhere in xfstests since the beginning.
> > > > > > Rewriting all scripts would be quite a lot of work, could you at least
> > > > > > provide safe versions of the cleanup helpers?
> > > > > 
> > > > > Hi David,
> > > > > 
> > > > > Thanks for taking care about it :)
> > > > > 
> > > > > > 
> > > > > > For example:
> > > > > > 
> > > > > > _rm_tmp() {
> > > > > >     rm -rf -- $tmp
> > > > > 
> > > > > It's "$tmp.*"
> > > > > 
> > > > > May I ask what problem does the "--" hope to avoid? If the "$tmp" is empty,
> > > > > "rm -rf" and "rm -rf --"" looks like both doing nothing. So what kind
> > > > > of situation does the "--" hope to fix?
> > > > > 
> > > > > The root problem in above [1] is about "${FOO}*". If someone does "rm -rf ${FOO}*"
> > > > > in its custom _cleanup_xxxxx function, then it's dangerous if "$FOO" is empty.
> > > > > 
> > > > > I thought some ways to avoid that:
> > > > > 1) Try to avoid doing rm -rf ${FOO}*, if not necessary.
> > > > > 2) Must checks [ -n "$FOO" ] before doing any rm -rf ${FOO}*
> > > > > 3) Someone's custom _cleanup_xxxxx better to be called before default _cleanup
> > > > > does "cd /".
> > > > > 4) Think about bringing in someone "Static program analysis" tool about bash
> > > > > script, but I don't know if there're someone good, feel free to give me
> > > > > suggestions.
> > > > 
> > > > "--" prevents the following arguments from being interpreted as options if they
> > > > begin with "-".  That's a good practice, but it doesn't help with ${FOO} being
> 
> Thanks Eric, I know "--" can do that, just didn't understand how it helps the
> empty variable problem. So looks like it doesn't.
> 
> > > > empty.  To cause the script to exit if ${FOO} is empty, it can be written as
> > > > ${FOO:?}.  Alternatively, 'set -u' can be used.
> > > 
> > > I said that four days ago.  Did nobody receive that reply?
> > > 
> > > https://lore.kernel.org/fstests/20240225165128.GA1128@sol.localdomain/T/#m0efd851c5a1fb0dbe418f4aff818d20f4355638b
> > > 
> > 
> > You didn't mention the :? option, and I thought that would be worth mentioning.

I wasn't even aware that existed.  It seems like a good way to enable
erroring on unset variable on a case by case basis.  Though TBH I
suspect that setting -u and using ${FOO:-} for the cases where we're
actually ok with unset variables is better practice.

Too bad it's going to be a lot of work to do /that/.

> Actually:
> 
> [ -n "$FOO" ] && rm -rf ${FOO}*
> 
> or
> 
> rm -rf ${FOO:?}*
> 
> Both of them are good to me, depends on what's expected. The 1st one ignore empty $FOO and
> keep running, the 2nd one breaks case running if $FOO is empty.
> 
> But they all need the programer to realize that his variable might be dangerous if
> it's empty, and write as that. So it still depends on the programer or the reviewers
> to notice that.

<nod>

--D

> Thanks,
> Zorro
> 
> > 
> > Of course ideally -u would be used everywhere, as you said.
> > 
> > - Eric
> > 
> 
>