Re: [RFC v3 0/3] VFS/NFS support to destroy FS credentials

[NeilBrown <neilb@suse.com>]

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On Thu, Aug 10 2017, Olga Kornievskaia wrote:

> On Wed, Aug 9, 2017 at 8:55 AM, David Howells <dhowells@redhat.com> wrote:
>> You may also want to flush any outstanding dirty data and wait for in-progress
>> operations.
>
> Sorry for the delayed response but I've been thinking about it as this
> is a tricky one (for me at least).
>
> Even currently, each file system needs a way to deal with flushing
> cached data to storage in the situation where creds might have expired
> in between when the kernel returned control back to the user but
> before all of buffered writes are flushed. NFS4.1 has wording in the
> spec for using machine credentials in that case.
>
> At the VFS layer, there no what to tell which dirty data belongs to
> which user. Flushing all data under the superblock seems like a bad
> idea?

NFS flushes data when the file descriptor is closed.  So as long as the
user does have any open-for-write file descriptors, their data should be
safe.  Purging credentials while you still have open-for-write file
descriptors is probably not a good idea.

This is not the case if you "nocto" mount option is used, but that is
recommended only for read-mostly mounts.

NeilBrown

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