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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Hoang Huu Le , Xiang Mei , Tung Quang Nguyen , linux-kernel@vger.kernel.org, Weiming Shi Subject: [PATCH net v3 2/2] tipc: fix NULL deref in tipc_named_node_up() on empty publication list Date: Tue, 14 Jul 2026 10:41:10 -0700 Message-ID: <20260714174110.1571033-3-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260714174110.1571033-1-bestswngs@gmail.com> References: <20260714174110.1571033-1-bestswngs@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit named_distribute() ends by stamping the last_bulk flag on the tail skb via buf_msg(skb_peek_tail(list)). When the publication list is empty no skb is enqueued, skb_peek_tail() returns NULL, and buf_msg(NULL) is dereferenced. tipc_named_node_up() runs this on &nt->cluster_scope. With a node-id configuration cluster_scope is populated only later by tipc_net_finalize(), so a peer link that comes up first reaches named_distribute() with an empty list. It is reachable by an unprivileged user (TIPC genl ops use GENL_UNS_ADMIN_PERM) over a UDP bearer in a user+net namespace: KASAN: null-ptr-deref in range [0x00000000000000d8-0x00000000000000df] RIP: 0010:tipc_named_node_up (net/tipc/name_distr.c:196) tipc_named_node_up (net/tipc/name_distr.c:196 net/tipc/name_distr.c:221) tipc_node_write_unlock (net/tipc/node.c:428) tipc_rcv (net/tipc/node.c:2185) tipc_udp_recv (net/tipc/udp_media.c:392) Kernel panic - not syncing: Fatal exception in interrupt The peer holds back this node's later name updates until it sees a bulk with the last_bulk flag, so simply skipping the empty bulk would stall it. Emit an item-less bulk when the list is empty, and break out of the build loop on allocation failure instead of returning, so the last_bulk flag is applied to the last queued skb. Fixes: cad2929dc432 ("tipc: update a binding service via broadcast") Reported-by: Xiang Mei Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Weiming Shi --- net/tipc/name_distr.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c index ba4f4906e13b..dbcfa965de34 100644 --- a/net/tipc/name_distr.c +++ b/net/tipc/name_distr.c @@ -165,7 +165,7 @@ static void named_distribute(struct net *net, struct sk_buff_head *list, dnode); if (!skb) { pr_warn("Bulk publication failure\n"); - return; + break; } hdr = buf_msg(skb); msg_set_bc_ack_invalid(hdr, true); @@ -192,6 +192,20 @@ static void named_distribute(struct net *net, struct sk_buff_head *list, skb_trim(skb, INT_H_SIZE + (msg_dsz - msg_rem)); __skb_queue_tail(list, skb); } + + if (skb_queue_empty(list)) { + skb = named_prepare_buf(net, PUBLICATION, 0, dnode); + if (!skb) { + pr_warn("Bulk publication failure\n"); + return; + } + hdr = buf_msg(skb); + msg_set_bc_ack_invalid(hdr, true); + msg_set_bulk(hdr); + msg_set_non_legacy(hdr); + __skb_queue_tail(list, skb); + } + hdr = buf_msg(skb_peek_tail(list)); msg_set_last_bulk(hdr); msg_set_named_seqno(hdr, seqno); -- 2.43.0