On 2018-10-13, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Sat, Oct 13, 2018 at 07:53:26PM +1100, Aleksa Sarai wrote: > > > I didn't know about path_is_under() -- I just checked and it appears to > > not take &rename_lock? From my understanding, in order to protect > > against the rename attack you need to take &rename_lock (or check > > against &rename_lock at least and retry if it changed). > > > > I could definitely use path_is_under() if you prefer, though I think > > that in this case we'd need to take &rename_lock (right?). Also is there > > a speed issue with taking the write-side of a seqlock when we are just > > reading -- is this more efficient than doing a retry like in __d_path? > > ??? > > 1) it uses is_subdir(), which does deal with rename_lock Oh -- complete brain-fart on my part. Sorry about that. > 2) what it does is taking mount_lock.lock. I.e. the same > thing as the second retry in __d_path(). _If_ it shows > up in profiles, we can switch it to read_seqbegin_or_lock(), > but I'd like to see the profiling data first. Sure, I'll switch it to use path_is_under(). -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/>
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