[krbdev.mit.edu #8651] kinit -kt KDB: Cannot find/read stored master key

[Richard Basch via RT]

I already implementing the workaround to use a file-based config after discovering the double-read.
I think the test for S_ISREG seems appropriate (just don’t use lstat since you want to follow symlinks).


> On Mar 18, 2018, at 4:05 PM, Greg Hudson via RT <rt-comment at krbdev.mit.edu> wrote:
> 
> The profile library is designed to automatically pick up changes to 
> the profile each time a profile_get_* call is made.  This feature is 
> of dubious usefulness, because our code base is inconsistent about 
> how long it caches profile results for, but I've been reluctant to 
> simplify it out.
> 
> To do this, it calls stat() and compares the mtime to the mtime from 
> the previous stat() result.  It does compare fractional timestamps, 
> so you would think the double-read would happen all the time (since 
> stat() on /dev/fd/NN appears to just give the current time).  
> However, there is also a guard against issuing too many stat() system 
> calls; at prof_file.c:316 we compare the current time to the last 
> time we read the filed or called stat(), and only issue a new stat() 
> call if the second has ticked over.
> 
> So I think in your scenario a failure only happens if the second 
> ticks over between the initial profile open and the profile read to 
> get the stash filename.
> 
> I think we could fix this scenario from our side by disabling the 
> stat-and-reread behavior for things that aren't regular files as 
> determined by S_ISREG().  From your side, you could of course work 
> around the issue by using a regular file.