Date: Tue, 31 Oct 2017 14:45:30 +0100 From: Solar Designer <solar@...nwall.com> To: oss-security@...ts.openwall.com Subject: Re: Fw: Security risk of vim swap files On Tue, Oct 31, 2017 at 01:50:36PM +0100, Stefan B??hler wrote: > On 10/31/2017 01:37 PM, Solar Designer wrote: > > On Tue, Oct 31, 2017 at 01:23:52PM +0100, Hanno B??ck wrote: > >> I think vim should change the behavior of swap files: > >> 1. they should be stored in /tmp by default > >> 2. they should have secure permissions (tmp file security is > >> a tricky thing and needs careful consideration to avoid symlink attacks > >> and the like, but there are dedicated functions for this like mkstemp). > >> 3. Ideally they also shouldn't leak currently edited filenames (e.g. > >> they shouldn't be called /tmp/.test.txt.swp, but more something > >> like /tmp/.vim_swap.123782173) > > > > Out of these, I think only 2 should be done: the files should be mode > > 0600 or 0400 even if the original file's permissions and/or the umask > > are more relaxed. > > > > 1 and 3 go against intended use for these files - recovery of an edit in > > progress if the editor or the entire system crashes (and comes back up > > e.g. after a power-cycle). /tmp contents might not survive a reboot, > > and randomized filenames would prevent vim itself from detecting the > > problem and offering recovery, which it does now. > > You could keep the .test.txt.swp file, but make it a symlink and encode > information where to find the real swap file (/var/tmp/, /tmp, ...) in > the symlink. > > It shouldn't link directly to the swap file, but perhaps look like > "swap:///var/tmp/.vim_swap.random_id". > > Instead of a symlink you could of course just create a normal text file > with the real swap filename in it, but then it might be easier for an > attacker to find the real filename and read that file. We could do a lot of things, but that doesn't mean those are good things to do. What you describe solves one of the problems I mentioned, but I see little reason to go for this extra complexity, partial breakage of vim's feature by default (/tmp and /var/tmp are commonly volatile), and added risks (and extra complexity to deal with them - checking the /var/tmp file's ownership and permissions in case it's been replaced by someone else after a reboot). Alexander
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