Re: [RFC] struct filename, io_uring and audit troubles

[Al Viro <viro@zeniv.linux.org.uk>]

On Mon, Sep 23, 2024 at 12:30:48AM -0600, Jens Axboe wrote:

> 1) Just don't reuse the entry. Then we can drop the struct
>    filename->aname completely as well. Yes that might incur an extra
>    alloc for the odd case of audit_enabled and being deep enough that
>    the preallocated names have been used, but doesn't anyone really
>    care? It'll be noise in the overhead anyway. Side note - that would
>    unalign struct filename again. Would be nice to drop audit_names from
>    a core fs struct...

You'll get different output in logs, though.  Whether that breaks userland
setups/invalidates certifications/etc.... fuck knows.

If anything, a loop through the list, searching for matching entry would
be safer in that respect.  Order of the items... might or might not be
an issue - see above.

> 2) Add a ref to struct audit_names, RCU kfree it when it drops to zero.
>    This would mean dropping struct audit_context->preallocated_names, as

Costly, that.

>    otherwise we'd run into trouble there if a context gets blown away
>    while someone else has a ref to that audit_names struct. We could do
>    this without a ref as well, as long as we can store an audit_context
>    pointer in struct audit_names and be able to validate it under RCU.
>    If ctx doesn't match, don't use it.

That's one of the variants I mentioned upthread...