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Wed, 29 Jul 2026 13:32:25 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 29 Jul 2026 16:32:22 -0400 Message-Id: To: "Michal Luczaj" , "Eric Dumazet" , "Kuniyuki Iwashima" , "Paolo Abeni" , "Willem de Bruijn" , "John Fastabend" , "Jakub Sitnicki" , "Jiayuan Chen" , "David S. Miller" , "Jakub Kicinski" , "Simon Horman" , "Daniel Borkmann" , "Stanislav Fomichev" , "Martin KaFai Lau" , "Alexei Starovoitov" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Emil Tsalapatis" , "Joe Stringer" Cc: , , , "Sashiko" Subject: Re: [PATCH bpf 3/3] bpf: Unconditionally take socket references in lookup helpers From: "Emil Tsalapatis" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260723-sockmap-lookup-tcp-leak-v1-0-1bbdc58ce514@rbox.co> <20260723-sockmap-lookup-tcp-leak-v1-3-1bbdc58ce514@rbox.co> In-Reply-To: <20260723-sockmap-lookup-tcp-leak-v1-3-1bbdc58ce514@rbox.co> On Thu Jul 23, 2026 at 7:33 AM EDT, Michal Luczaj wrote: > Lookup helpers gate whether to acquire a socket reference on > sk_is_refcounted(), a check re-evaluated at release. An established socke= t > refcounted at acquire time can gain SOCK_RCU_FREE via > connect(AF_UNSPEC)+listen() before release runs; the release-side re-chec= k > then reads sk_is_refcounted() =3D=3D false and skips the put. The referen= ce > leaks. > > Make acquire and release unconditional and symmetric: always take a > reference, always put it. Adapt sk_select_reuseport(). Reviewed-by: Emil Tsalapatis The bot's concern about the comment style is obviously invalid here. > > Fixes: 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF") > Fixes: 64d85290d79c ("bpf: Allow bpf_map_lookup_elem for SOCKMAP and SOCK= HASH") > Reported-by: Sashiko > Closes: https://lore.kernel.org/bpf/20260701235552.2B0AA1F00A3F@smtp.kern= el.org/ > Signed-off-by: Michal Luczaj > --- > net/core/filter.c | 25 ++++++++++++++++--------- > net/core/sock_map.c | 8 ++------ > 2 files changed, 18 insertions(+), 15 deletions(-) > > diff --git a/net/core/filter.c b/net/core/filter.c > index 403aba3ce891..4bc0b59668fa 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -7027,6 +7027,13 @@ static struct sock *sk_lookup(struct net *net, str= uct bpf_sock_tuple *tuple, > WARN_ONCE(1, "Found non-RCU, unreferenced socket!"); > sk =3D NULL; > } > + > + /* Always take a reference, even if the lookup skipped one; > + * bpf_sk_release() always puts one. > + */ > + if (sk && !refcounted && !refcount_inc_not_zero(&sk->sk_refcnt)) > + sk =3D NULL; > + > return sk; > } > =20 > @@ -7084,11 +7091,15 @@ bpf_sk_lookup_full_sk(struct sock *sk) > */ > if (sk2 !=3D sk) { > sock_gen_put(sk); > - /* Ensure there is no need to bump sk2 refcnt. */ > if (unlikely(sk2 && !sock_flag(sk2, SOCK_RCU_FREE))) { > WARN_ONCE(1, "Found non-RCU, unreferenced socket!"); > return NULL; > } > + /* sk2 is RCU-free, but take a reference anyway; > + * bpf_sk_release() puts. > + */ > + if (sk2 && !refcount_inc_not_zero(&sk2->sk_refcnt)) > + sk2 =3D NULL; > sk =3D sk2; > } > =20 > @@ -7273,7 +7284,7 @@ static const struct bpf_func_proto bpf_tc_sk_lookup= _udp_proto =3D { > =20 > BPF_CALL_1(bpf_sk_release, struct sock *, sk) > { > - if (sk && sk_is_refcounted(sk)) > + if (sk) > sock_gen_put(sk); > return 0; > } > @@ -11565,11 +11576,13 @@ BPF_CALL_4(sk_select_reuseport, struct sk_reuse= port_kern *, reuse_kern, > bool is_sockarray =3D map->map_type =3D=3D BPF_MAP_TYPE_REUSEPORT_SOCKA= RRAY; > struct sock_reuseport *reuse; > struct sock *selected_sk; > - int err; > + int err =3D 0; > =20 > selected_sk =3D map->ops->map_lookup_elem(map, key); > if (!selected_sk) > return -ENOENT; > + if (!is_sockarray) > + sock_put(selected_sk); > =20 > reuse =3D rcu_dereference(selected_sk->sk_reuseport_cb); > if (!reuse) { > @@ -11599,13 +11612,7 @@ BPF_CALL_4(sk_select_reuseport, struct sk_reusep= ort_kern *, reuse_kern, > } > =20 > reuse_kern->selected_sk =3D selected_sk; > - > - return 0; > error: > - /* Lookup in sock_map can return TCP ESTABLISHED sockets. */ > - if (sk_is_refcounted(selected_sk)) > - sock_put(selected_sk); > - > return err; > } > =20 > diff --git a/net/core/sock_map.c b/net/core/sock_map.c > index ca49bc7f8687..ae18dc4d60f9 100644 > --- a/net/core/sock_map.c > +++ b/net/core/sock_map.c > @@ -390,9 +390,7 @@ static void *sock_map_lookup(struct bpf_map *map, voi= d *key) > struct sock *sk; > =20 > sk =3D __sock_map_lookup_elem(map, *(u32 *)key); > - if (!sk) > - return NULL; > - if (sk_is_refcounted(sk)) > + if (sk) > sock_hold(sk); > return sk; > } > @@ -1216,9 +1214,7 @@ static void *sock_hash_lookup(struct bpf_map *map, = void *key) > struct sock *sk; > =20 > sk =3D __sock_hash_lookup_elem(map, key); > - if (!sk) > - return NULL; > - if (sk_is_refcounted(sk)) > + if (sk) > sock_hold(sk); > return sk; > }