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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43b51892244sm9738790f8f.22.2026.03.18.09.24.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 09:24:23 -0700 (PDT) From: David Carlier To: Alexei Starovoitov , Daniel Borkmann , davem@davemloft.net, Jakub Kicinski Cc: netdev@vger.kernel.org, David Carlier Subject: [PATCH] bpf: use RCU-safe iteration in dev_map_redirect_multi() SKB path Date: Wed, 18 Mar 2026 16:24:20 +0000 Message-ID: <20260318162420.7684-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The DEVMAP_HASH branch in dev_map_redirect_multi() uses hlist_for_each_entry_safe() to iterate hash buckets, but this function runs under RCU protection (called from xdp_do_generic_redirect_map() in softirq context). Concurrent writers (__dev_map_hash_update_elem, dev_map_hash_delete_elem) modify the list using RCU primitives (hlist_add_head_rcu, hlist_del_rcu). hlist_for_each_entry_safe() performs plain pointer dereferences without rcu_dereference(), missing the acquire barrier needed to pair with writers' rcu_assign_pointer(). On weakly-ordered architectures (ARM64, POWER), a reader can observe a partially-constructed node. It also defeats CONFIG_PROVE_RCU lockdep validation and KCSAN data-race detection. Replace with hlist_for_each_entry_rcu(), matching the XDP-frame path (dev_map_enqueue_multi) which already uses the correct macro for the same hash iteration. Fixes: e624d4ed4aa8 ("xdp: Extend xdp_redirect_map with broadcast support") Signed-off-by: David Carlier --- kernel/bpf/devmap.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c index 3d619d01088e..c8d256405c29 100644 --- a/kernel/bpf/devmap.c +++ b/kernel/bpf/devmap.c @@ -747,7 +747,6 @@ int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb, struct bpf_dtab_netdev *dst, *last_dst = NULL; int excluded_devices[1+MAX_NEST_DEV]; struct hlist_head *head; - struct hlist_node *next; int num_excluded = 0; unsigned int i; int err; @@ -787,7 +786,7 @@ int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb, } else { /* BPF_MAP_TYPE_DEVMAP_HASH */ for (i = 0; i < dtab->n_buckets; i++) { head = dev_map_index_hash(dtab, i); - hlist_for_each_entry_safe(dst, next, head, index_hlist) { + hlist_for_each_entry_rcu(dst, head, index_hlist, lockdep_is_held(&dtab->index_lock)) { if (is_ifindex_excluded(excluded_devices, num_excluded, dst->dev->ifindex)) continue; -- 2.53.0