From: Salvatore Mesoraca [mailto:s.mesoraca16@xxxxxxxxx] > Sent: 24 November 2017 11:44 > > 2017-11-24 11:53 GMT+01:00 David Laight <David.Laight@xxxxxxxxxx>: > > From: Alan Cox > >> Sent: 22 November 2017 16:52 > >> > >> On Wed, 22 Nov 2017 09:01:46 +0100 > >> Salvatore Mesoraca <s.mesoraca16@xxxxxxxxx> wrote: > >> > >> > Disallows O_CREAT open missing the O_EXCL flag, in world or > >> > group writable directories, even if the file doesn't exist yet. > >> > With few exceptions (e.g. shared lock files based on flock()) > >> > >> Enough exceptions to make it a bad idea. > >> > >> Firstly if you care this much *stop* having shared writable directories. > >> We have namespaces, you don't need them. You can give every user their > >> own /tmp etc. > > > > Looks like a very bad idea to me as well. > > > > Doesn't this stop all shell redirects into a shared /tmp ? > > I'm pretty sure most programs use O_CREAT | O_TRUNC for output > > files - they'll all stop working. > > If some program does such a thing, that's a potential vulnerability. > With "protected_hardlinks" you are, in most cases, safe. > But, still, that program has a bug and having this feature enabled will > help you notice it soon. > For that matter, I'm using this patch on my system and I don't have any > program behaving like this. Hmmm.... a quick strace shows cp and vi doing stat("/tmp/foo") and then open(O_WRONLY|O_TRUNC) if it exists and O_CREATE|O_EXCL if it doesn't. I can't help feeling that is just hiding a race. David
