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Date: Tue, 14 Jan 2020 16:48:23 +0100 From: Jakub Sitnicki <jakub@...udflare.com> To: Martin Lau <kafai@...com>, John Fastabend <john.fastabend@...il.com> Cc: "bpf\@vger.kernel.org" <bpf@...r.kernel.org>, "netdev\@vger.kernel.org" <netdev@...r.kernel.org>, "kernel-team\@cloudflare.com" <kernel-team@...udflare.com>, Eric Dumazet <edumazet@...gle.com>, Lorenz Bauer <lmb@...udflare.com> Subject: Re: [PATCH bpf-next v2 07/11] bpf, sockmap: Return socket cookie on lookup from syscall On Tue, Jan 14, 2020 at 04:16 AM CET, John Fastabend wrote: > Martin Lau wrote: >> On Fri, Jan 10, 2020 at 11:50:23AM +0100, Jakub Sitnicki wrote: >> > Tooling that populates the SOCKMAP with sockets from user-space needs a way >> > to inspect its contents. Returning the struct sock * that SOCKMAP holds to >> > user-space is neither safe nor useful. An approach established by >> > REUSEPORT_SOCKARRAY is to return a socket cookie (a unique identifier) >> > instead. >> > >> > Since socket cookies are u64 values SOCKMAP needs to support such a value >> > size for lookup to be possible. This requires special handling on update, >> > though. Attempts to do a lookup on SOCKMAP holding u32 values will be met >> > with ENOSPC error. >> > >> > Signed-off-by: Jakub Sitnicki <jakub@...udflare.com> >> > --- > > [...] > >> > +static void *sock_map_lookup_sys(struct bpf_map *map, void *key) >> > +{ >> > + struct sock *sk; >> > + >> > + WARN_ON_ONCE(!rcu_read_lock_held()); >> It seems unnecessary. It is only called by syscall.c which >> holds the rcu_read_lock(). Other than that, >> > > +1 drop it. The normal rcu annotations/splats should catch anything > here. Oh, okay. Thanks for pointing it out. I noticed __sock_map_lookup_elem called from sock_map_lookup_sys has the same WARN_ON_ONCE check. Looks like it can be cleaned up. Granted, __sock_map_lookup_elem also gets invoked by sockmap BPF helpers for redirecting (bpf_msg_redirect_map, bpf_sk_redirect_map). But we always run sk_skb and sk_msg progs RCU read lock held.
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