{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-72404", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-72404" ], "published": "2026-08-15T06:04:33Z", "summary": "tipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()\n\nTIPC UDP media bearer teardown calls dst_cache_destroy() on its\nreplicast caches before calling synchronize_net() to wait for\nconcurrent RCU readers (transmitters) to finish:\n\nstatic void cleanup_bearer(struct work_struct *work)\n{\n...\n\tlist_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {\n\t\tdst_cache_destroy(&rcast->dst_cache);\n\t\tlist_del_rcu(&rcast->list);\n\t\tkfree_rcu(rcast, rcu);\n\t}\n...\n\tdst_cache_destroy(&ub->rcast.dst_cache);\n\tudp_tunnel_sock_release(ub->sk);\n\tsynchronize_net();\n...\n}\n\nThis is highly buggy because dst_cache_destroy() immediately frees the\nper-CPU cache memory (free_percpu()) and releases the cached dst\nentries without any synchronization.\n\nIf a concurrent transmitter (e.g., tipc_udp_xmit()) is running on another\nCPU under RCU protection, it can call dst_cache_get() concurrently,\nleading to:\n1. Use-After-Free on the per-CPU cache pointer itself (crash).\n2. \"rcuref - imbalanced put()\" warning if it attempts to release a\n dst that was concurrently released by dst_cache_destroy().\n\nFurthermore, calling kfree(ub) immediately after synchronize_net() without\nclosing the socket first (or waiting after closing it) leaves a window\nwhere a concurrent receiver (tipc_udp_recv()) could start after\nsynchronize_net(), access ub, and suffer a UAF when kfree(ub) runs.\n\nTo fix this, we must defer dst_cache_destroy() and kfree(ub) until after\nwe have ensured that no more readers can see the bearer/socket and all\nexisting readers have finished:\n\n1. Defer rcast entry destruction (both dst_cache_destroy() and kfree())\n to an RCU callback using call_rcu_hurry().\n Using call_rcu_hurry() ensures the dst entries are released quickly.\n\n2. Release the bearer socket using udp_tunnel_sock_release() (stops\n new receive readers).\n\n3. Call synchronize_net() to wait for all outstanding RCU readers\n (both transmit and receive) to finish.\n\n4. Now that it is safe, call dst_cache_destroy() on the main bearer\n cache, and free ub.\n\nNote: 3) and 4) can be changed later in net-next to also use\ncall_rcu_hurry() and get rid of the synchronize_net() latency.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": null, "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-72404" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/7116764ca53ff529335d7ab7c364a69f094b23a5" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-17T05:50:24Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The UAF is in cleanup_bearer() during UDP bearer teardown, reached only via TIPC genetlink bearer disable (TIPC_NL_BEARER_DISABLE) or network-namespace exit; remote UDP/TIPC peers cannot initiate teardown, so exploitation requires local netlink/netns access even though concurrent xmit/recv may involve network I/O.\nAC:L - An attacker with namespace CAP_NET_ADMIN can script both teardown and concurrent traffic (enable/disable bearer or destroy netns while sending/receiving TIPC UDP on port 6118), controlling both sides of the RCU race; dst_cache_destroy()'s free_percpu() widens the window and syzbot triggered it reliably.\nPR:L - Bearer disable/enable and netns teardown require CAP_NET_ADMIN; TIPC genetlink ops use GENL_UNS_ADMIN_PERM and tipc_genl_family.netnsok=true, so unprivileged users obtain effective net-admin capability via user/network namespaces (unshare -Urn).\nUI:N - Exploitation needs no victim interaction beyond the attacker's own namespace/netlink operations and packet generation; no mount, file open, or other user-directed action is required.\nS:U - The use-after-free corrupts kernel heap memory within the same kernel security domain; impacts are kernel crash or local privilege escalation, not VM escape or cross-security-authority boundary crossing.\nC:H - Premature dst_cache_destroy() frees per-CPU cache memory while concurrent tipc_udp_xmit() may call dst_cache_get() on the freed object, and the post-synchronize_net() recv path dereferences freed udp_bearer, enabling kernel memory disclosure.\nI:H - UAF on dst_cache structures and udp_bearer allows heap shaping and control of freed-object contents, providing primitives for arbitrary kernel writes and potential control-flow hijacking/local privilege escalation.\nA:H - Concurrent use-after-free reliably causes kernel oops/panic (per commit: UAF on per-CPU cache pointer crashes) and can be triggered repeatedly during scripted bearer teardown loops." } } }