GHSA-XHXF-MW58-XFPX
Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-10-15 12:30In the Linux kernel, the following vulnerability has been resolved:
tipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()
TIPC UDP media bearer teardown calls dst_cache_destroy() on its replicast caches before calling synchronize_net() to wait for concurrent RCU readers (transmitters) to finish:
static void cleanup_bearer(struct work_struct *work) { ... list_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) { dst_cache_destroy(&rcast->dst_cache); list_del_rcu(&rcast->list); kfree_rcu(rcast, rcu); } ... dst_cache_destroy(&ub->rcast.dst_cache); udp_tunnel_sock_release(ub->sk); synchronize_net(); ... }
This is highly buggy because dst_cache_destroy() immediately frees the per-CPU cache memory (free_percpu()) and releases the cached dst entries without any synchronization.
If a concurrent transmitter (e.g., tipc_udp_xmit()) is running on another CPU under RCU protection, it can call dst_cache_get() concurrently, leading to: 1. Use-After-Free on the per-CPU cache pointer itself (crash). 2. "rcuref - imbalanced put()" warning if it attempts to release a dst that was concurrently released by dst_cache_destroy().
Furthermore, calling kfree(ub) immediately after synchronize_net() without closing the socket first (or waiting after closing it) leaves a window where a concurrent receiver (tipc_udp_recv()) could start after synchronize_net(), access ub, and suffer a UAF when kfree(ub) runs.
To fix this, we must defer dst_cache_destroy() and kfree(ub) until after we have ensured that no more readers can see the bearer/socket and all existing readers have finished:
-
Defer rcast entry destruction (both dst_cache_destroy() and kfree()) to an RCU callback using call_rcu_hurry(). Using call_rcu_hurry() ensures the dst entries are released quickly.
-
Release the bearer socket using udp_tunnel_sock_release() (stops new receive readers).
-
Call synchronize_net() to wait for all outstanding RCU readers (both transmit and receive) to finish.
-
Now that it is safe, call dst_cache_destroy() on the main bearer cache, and free ub.
Note: 3) and 4) can be changed later in net-next to also use call_rcu_hurry() and get rid of the synchronize_net() latency.
{
"affected": [],
"aliases": [
"CVE-2026-72404"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-15T06:22:13Z",
"severity": "HIGH"
},
"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, \u0026ub-\u003ercast.list, list) {\n\t\tdst_cache_destroy(\u0026rcast-\u003edst_cache);\n\t\tlist_del_rcu(\u0026rcast-\u003elist);\n\t\tkfree_rcu(rcast, rcu);\n\t}\n...\n\tdst_cache_destroy(\u0026ub-\u003ercast.dst_cache);\n\tudp_tunnel_sock_release(ub-\u003esk);\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.",
"id": "GHSA-xhxf-mw58-xfpx",
"modified": "2026-10-15T12:30:41Z",
"published": "2026-08-15T06:32:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72404"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1c8393eefa3cadf4ca0b61119ad1321aa32d3c8c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3827ff67f9fbecd1086e33d23693ef6a1a9c6c38"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7116764ca53ff529335d7ab7c364a69f094b23a5"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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