Re: [PATCH net v2 1/1] udp: diag: bound bucket lock hold time

[zihan xi]

On Mon, Sep 7, 2026 at 3:07 PM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Sun, Sep 6, 2026 at 12:35 PM Zihan Xi <zihanx@xxxxxxxxxx> wrote:
> >
> > udp_diag_dump() currently keeps the UDP hash bucket spinlock held while
> > running the request's bytecode filter and filling a netlink response for
> > every socket in the bucket.  A large filter and a heavily populated bucket
> > can therefore keep bottom halves disabled for an attacker-scaled amount of
> > time.
> >
> > Collect at most SKARR_SZ matching sockets under the bucket lock, taking a
> > reference for each socket, then run the filter and fill the response after
> > releasing the lock.  Resume with the existing (slot, s_num) dump state so
> > the next batch can skip already-walked sockets.  Leave bytecode filtering
> > until after unlock; unlike tcp_diag, a rejecting inet_diag bytecode program
> > is the expensive part of this walk.
> >
> > Fixes: b6d640c2286d ("udp_diag: Implement the dump-all functionality")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Reported-by: Vega <vega@xxxxxxxxxx>
> > Assisted-by: LLM
> > Signed-off-by: Zihan Xi <zihanx@xxxxxxxxxx>
> > ---
> > changes in v2:
> >   - Drop the hash-list cursor, dump_done callback, extra module
> >     reference, and inet_diag core changes.  Dump state is only
> >     (slot, s_num), so the existing handler get/put around dump() is
> >     enough and udp_diag no longer manages its own module lifetime.
> >   - Batch at most SKARR_SZ matching sockets under the bucket lock
> >     like tcp_diag, and run bytecode filtering plus netlink fill after
> >     unlock.
> >   - v1 Link: https://lore.kernel.org/all/133b6aee9e2c908c9da37d5585b3d2cd016906cd.1788187473.git.zihanx@xxxxxxxxxx
>
> pw-bot: rejected
>
> Please limit the complexity of filters.
>
> Anywone needing complex filters will implement them in user space.

Agreed.  v2 tried to make the dump walk tolerate large bytecode;
that was the wrong approach.

I will drop this patch and send a new series that rejects oversized
programs in inet_diag_bc_audit().  Richer matching can stay in
userspace.