> On Tue, Jan 10, 2023 at 06:58:15PM +0100, Jakub Wilk wrote:
> > If you edit a foo.gz file from a directory which is not writable by you, Vim
> > tries to use /var/tmp/foo.gz.swp as the swap file,
>
> Vim prefers to use ~/tmp/foo.gz.swp, but it won't create ~/tmp for you.
This reminds me that the default value for 'directory' is not good for a
multi-user system. However, it's not so easy to come up with an
alternative that will work everywhere.
> As for why this is happening with .gz files, I think it's because
> gzip#read does end up writing a file. Refactoring the plugin to use
> the BufReadCmd, BufWriteCmd, etc. might help avoid this.
It will still need to write a file, so that the uncompress command can
read it.
> > even when this file
> > already exist and is owned by somebody else.
>
> One of the main purposes of swap files is to detect when someone else is
> editing the same file and warn you. Therefore, Vim has to try reading
> the potential swapfile.
If the file exist then Vim will use ".swo" instead of ".swp". Anyway,
it would still be in the public "tmp" directory, thus this is just a
detail.
> Vim could try checking for non-regular files first, which would swap the
> naive problem here with one that requires a race to replace the file
> after it's checked.
>
> Arguably, Vim should use the // form for any directory other than ".":
>
> - For Unix and Win32, if a directory ends in two path separators "//",
> the swap file name will be built from the complete path to the file
> with all path separators replaced by percent '%' signs (including
> the colon following the drive letter on Win32). This will ensure
> file name uniqueness in the preserve directory.
>
> However, this just reduces chance of collisions, not the overall gist
> behind your reproduction.
>
> > This can be exploited for
> > denial of service, maybe worse.
> >
> > To reproduce, run:
> >
> > mkfifo -m 666 /var/tmp/changelog.gz.swp
> >
> > Then, as another user:
> >
> > vim /usr/share/doc/vim/changelog.gz
> >
> > Vim will hang forever (and can't be killed easily).
Also, others can read the swap file, something the user probably isn't
aware of.
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