ghsa-wq9h-7v97-wgcp
Vulnerability from github
Published
2024-09-04 21:30
Modified
2024-10-09 15:32
Severity ?
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Details

In the Linux kernel, the following vulnerability has been resolved:

tcp: prevent concurrent execution of tcp_sk_exit_batch

Its possible that two threads call tcp_sk_exit_batch() concurrently, once from the cleanup_net workqueue, once from a task that failed to clone a new netns. In the latter case, error unwinding calls the exit handlers in reverse order for the 'failed' netns.

tcp_sk_exit_batch() calls tcp_twsk_purge(). Problem is that since commit b099ce2602d8 ("net: Batch inet_twsk_purge"), this function picks up twsk in any dying netns, not just the one passed in via exit_batch list.

This means that the error unwind of setup_net() can "steal" and destroy timewait sockets belonging to the exiting netns.

This allows the netns exit worker to proceed to call

WARN_ON_ONCE(!refcount_dec_and_test(&net->ipv4.tcp_death_row.tw_refcount));

without the expected 1 -> 0 transition, which then splats.

At same time, error unwind path that is also running inet_twsk_purge() will splat as well:

WARNING: .. at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210 ... refcount_dec include/linux/refcount.h:351 [inline] inet_twsk_kill+0x758/0x9c0 net/ipv4/inet_timewait_sock.c:70 inet_twsk_deschedule_put net/ipv4/inet_timewait_sock.c:221 inet_twsk_purge+0x725/0x890 net/ipv4/inet_timewait_sock.c:304 tcp_sk_exit_batch+0x1c/0x170 net/ipv4/tcp_ipv4.c:3522 ops_exit_list+0x128/0x180 net/core/net_namespace.c:178 setup_net+0x714/0xb40 net/core/net_namespace.c:375 copy_net_ns+0x2f0/0x670 net/core/net_namespace.c:508 create_new_namespaces+0x3ea/0xb10 kernel/nsproxy.c:110

... because refcount_dec() of tw_refcount unexpectedly dropped to 0.

This doesn't seem like an actual bug (no tw sockets got lost and I don't see a use-after-free) but as erroneous trigger of debug check.

Add a mutex to force strict ordering: the task that calls tcp_twsk_purge() blocks other task from doing final _dec_and_test before mutex-owner has removed all tw sockets of dying netns.

Show details on source website

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{
   affected: [],
   aliases: [
      "CVE-2024-44991",
   ],
   database_specific: {
      cwe_ids: [],
      github_reviewed: false,
      github_reviewed_at: null,
      nvd_published_at: "2024-09-04T20:15:08Z",
      severity: "MODERATE",
   },
   details: "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: prevent concurrent execution of tcp_sk_exit_batch\n\nIts possible that two threads call tcp_sk_exit_batch() concurrently,\nonce from the cleanup_net workqueue, once from a task that failed to clone\na new netns.  In the latter case, error unwinding calls the exit handlers\nin reverse order for the 'failed' netns.\n\ntcp_sk_exit_batch() calls tcp_twsk_purge().\nProblem is that since commit b099ce2602d8 (\"net: Batch inet_twsk_purge\"),\nthis function picks up twsk in any dying netns, not just the one passed\nin via exit_batch list.\n\nThis means that the error unwind of setup_net() can \"steal\" and destroy\ntimewait sockets belonging to the exiting netns.\n\nThis allows the netns exit worker to proceed to call\n\nWARN_ON_ONCE(!refcount_dec_and_test(&net->ipv4.tcp_death_row.tw_refcount));\n\nwithout the expected 1 -> 0 transition, which then splats.\n\nAt same time, error unwind path that is also running inet_twsk_purge()\nwill splat as well:\n\nWARNING: .. at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210\n...\n refcount_dec include/linux/refcount.h:351 [inline]\n inet_twsk_kill+0x758/0x9c0 net/ipv4/inet_timewait_sock.c:70\n inet_twsk_deschedule_put net/ipv4/inet_timewait_sock.c:221\n inet_twsk_purge+0x725/0x890 net/ipv4/inet_timewait_sock.c:304\n tcp_sk_exit_batch+0x1c/0x170 net/ipv4/tcp_ipv4.c:3522\n ops_exit_list+0x128/0x180 net/core/net_namespace.c:178\n setup_net+0x714/0xb40 net/core/net_namespace.c:375\n copy_net_ns+0x2f0/0x670 net/core/net_namespace.c:508\n create_new_namespaces+0x3ea/0xb10 kernel/nsproxy.c:110\n\n... because refcount_dec() of tw_refcount unexpectedly dropped to 0.\n\nThis doesn't seem like an actual bug (no tw sockets got lost and I don't\nsee a use-after-free) but as erroneous trigger of debug check.\n\nAdd a mutex to force strict ordering: the task that calls tcp_twsk_purge()\nblocks other task from doing final _dec_and_test before mutex-owner has\nremoved all tw sockets of dying netns.",
   id: "GHSA-wq9h-7v97-wgcp",
   modified: "2024-10-09T15:32:18Z",
   published: "2024-09-04T21:30:32Z",
   references: [
      {
         type: "ADVISORY",
         url: "https://nvd.nist.gov/vuln/detail/CVE-2024-44991",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/565d121b69980637f040eb4d84289869cdaabedf",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/99580ae890ec8bd98b21a2a9c6668f8f1555b62e",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/e3d9de3742f4d5c47ae35f888d3023a5b54fcd2f",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/f6fd2dbf584a4047ba88d1369ff91c9851261ec1",
      },
   ],
   schema_version: "1.4.0",
   severity: [
      {
         score: "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
         type: "CVSS_V3",
      },
   ],
}


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