KSaveFile

[Julian Rockey]

On Monday 23 Feb 2004 11:07, Jörg Walter wrote:
> On Saturday, 21. February 2004 22:20, Richard Smith wrote:
> > On Saturday 21 February 2004 9:13 pm, Waldo Bastian wrote:
> > > On Sat February 21 2004 18:01, Julian Rockey wrote:
>
> [...]
>
> There's still a race condition in your model. You should open() it with
> mode 0600 and then chmod, otherwise this can happen (B is the attacker):
>
> 1. A opens file, mode 0644 (or whatever umask is set)
But I thought mkstemps creates the file with 0600? (at least in recent 
glibc's)
cheers
Julian

> 2. B opens file immediately thereafter, is granted the open, but file is
> empty 3. A chmods to 0600, then writes, finally renames
> 4. B is still allowed to read
>
> (very small timeframe to get at it, but DNOTIFY makes these timing attacks
> work quite reliably)
>
> Solution: Pass mode 0600 to open(), since you're chmodding afterwards
> anyways.
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