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Thu, 24 Sep 2026 19:00:29 -0700 (PDT) Received: from localhost.localdomain ([175.159.181.20]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a0ba31f408sm369914a91.3.2026.09.24.19.00.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 19:00:28 -0700 (PDT) From: Yu Junzhe To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , Sasha Levin , Pablo Neira Ayuso , Florian Westphal , netfilter-devel@vger.kernel.org Subject: [PATCH request stable 6.12 6.6 6.1] netfilter: nf_tables_netdev_event UAF of binding chain Date: Fri, 25 Sep 2026 02:00:25 +0000 Message-ID: <20260925020025.616-1-junzheyu1@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hello, Please consider a backport of the following use-after-free to the longterm trees that still have it: 6.12, 6.6, and 6.1. 6.18 and newer are not affected. There is no single upstream commit to cherry-pick. On current linux.git the netdev notifier no longer calls __nft_release_basechain(); it only unregisters the per-device hook. That change arrived as part of the netdev-hook rework and does not apply to these stable trees. Bug === nf_tables_netdev_event() walks table->chains with list_for_each_entry_safe. On NETDEV_UNREGISTER of the last hook, nft_netdev_event() calls __nft_release_basechain(). Releasing the base chain deactivates a JUMP to an NFT_CHAIN_BINDING chain, which nft_chain_del()s that successor and nft_immediate_destroy() kfree()s it. The walker's saved nr still points at the freed nft_chain. Still present in: linux-6.12.y (6.12.111) nft_chain_filter.c: __nft_release_basechain() linux-6.6.y (6.6.157) linux-6.1.y (6.1.188) Gone in linux-6.18.y and linux-7.0.y. Reproducer (nftables 1.0.9) =========================== An anonymous jump is what sets NFT_CHAIN_BINDING (chain flags 0x4). Commit the base chain first, then add the jump in a second command. Chains are appended to table->chains, and the walker frees the chain that follows the base chain. One nft -f that contains both creates the binding chain first and does not hit this path. ip link add br0 type bridge ip link set br0 up nft -f - <<'EOF' table netdev t { chain in { type filter hook ingress device "br0" priority 0; policy accept; } } EOF nft add rule netdev t in 'jump { accept; }' ip link del br0 The namespace must still be alive. Netns teardown is too late: nft pernet exit wins that race. Needs CAP_NET_ADMIN. Do not run on a host kernel. Confirmed on Linux 6.6.144 KASAN (same __nft_release_basechain() walk as 6.6.y and 6.12.y). I have not booted 6.12.111 or 6.1.188. BUG: KASAN: slab-use-after-free in nf_tables_netdev_event+0x635/0x970 Read of size 8 at addr ff110000037faa20 by task ip/229 Freed by task 229: nft_immediate_destroy __nft_release_basechain_now __nft_release_basechain nf_tables_netdev_event The read is 8 bytes at offset 32 of a kmalloc-128 object (nft_chain.list). Thanks, Yu Junzhe FuzzAnything