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Miller" , Eric Dumazet , Paolo Abeni Cc: Pablo Neira Ayuso , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Xiang Mei , Weiming Shi , stable@vger.kernel.org Subject: [PATCH net] netdevsim: tc: serialize access to nsim_block_cb_list Date: Sun, 19 Jul 2026 10:50:29 -0700 Message-ID: <20260719175028.988301-2-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nsim_setup_tc() passes a single global nsim_block_cb_list, shared by every netdevsim device, to flow_block_cb_setup_simple(). That helper does list_add_tail()/list_del() on the list on block bind/unbind and walks it in flow_block_cb_is_busy(); it takes no lock of its own and relies on the caller for serialization. The tc control path calls ndo_setup_tc(TC_SETUP_BLOCK) under rtnl, but the nf_tables hardware offload path reaches it under the per-netns nftables commit_mutex only. Two nft transactions committing offload chains from different netns thus run flow_block_cb_setup_simple() on the same list concurrently, corrupting it and freeing a flow_block_cb that the other CPU still walks: list_del corruption. prev->next should be ffff88801f18ff00, but was ffff88801de82b00. kernel BUG at lib/list_debug.c:62! RIP: 0010:__list_del_entry_valid_or_report (lib/list_debug.c:62) flow_block_cb_setup_simple (net/core/flow_offload.c:369) nsim_setup_tc (drivers/net/netdevsim/tc.c) nft_block_offload_cmd (net/netfilter/nf_tables_offload.c:394) nft_flow_rule_offload_commit (net/netfilter/nf_tables_offload.c:585) nf_tables_commit (net/netfilter/nf_tables_api.c:10490) nfnetlink_rcv_batch (net/netfilter/nfnetlink.c:577) nfnetlink_rcv (net/netfilter/nfnetlink.c:649) netlink_unicast (net/netlink/af_netlink.c:1314) netlink_sendmsg (net/netlink/af_netlink.c:1889) __sys_sendto (net/socket.c:729) With KASAN the same race is reported as a slab-use-after-free read of the freed flow_block_cb (kmalloc-192) in flow_block_cb_setup_simple(). The trace above is from a 6.12.y reproduction. Serialize the list with a mutex. ndo_setup_tc(TC_SETUP_BLOCK) always runs in process context, so sleeping on the mutex is fine. Fixes: 955bcb6ea0df ("drivers: net: use flow block API") Reported-by: Xiang Mei Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Weiming Shi --- drivers/net/netdevsim/tc.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/drivers/net/netdevsim/tc.c b/drivers/net/netdevsim/tc.c index a415e02a6df1..30dd7f924b71 100644 --- a/drivers/net/netdevsim/tc.c +++ b/drivers/net/netdevsim/tc.c @@ -72,11 +72,13 @@ static int nsim_setup_tc_ets(struct net_device *dev, } static LIST_HEAD(nsim_block_cb_list); +static DEFINE_MUTEX(nsim_block_cb_lock); int nsim_setup_tc(struct net_device *dev, enum tc_setup_type type, void *type_data) { struct netdevsim *ns = netdev_priv(dev); + int err; switch (type) { case TC_SETUP_QDISC_TAPRIO: @@ -84,10 +86,13 @@ nsim_setup_tc(struct net_device *dev, enum tc_setup_type type, void *type_data) case TC_SETUP_QDISC_ETS: return nsim_setup_tc_ets(dev, type_data); case TC_SETUP_BLOCK: - return flow_block_cb_setup_simple(type_data, - &nsim_block_cb_list, - nsim_setup_tc_block_cb, - ns, ns, true); + mutex_lock(&nsim_block_cb_lock); + err = flow_block_cb_setup_simple(type_data, + &nsim_block_cb_list, + nsim_setup_tc_block_cb, + ns, ns, true); + mutex_unlock(&nsim_block_cb_lock); + return err; case TC_SETUP_FT: return 0; default: -- 2.43.0