ghsa-8x8h-8p2w-8g4f
Vulnerability from github
Published
2024-04-03 18:30
Modified
2024-11-04 21:30
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:

bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel

The following race is possible between bpf_timer_cancel_and_free and bpf_timer_cancel. It will lead a UAF on the timer->timer.

bpf_timer_cancel(); spin_lock(); t = timer->time; spin_unlock();

                bpf_timer_cancel_and_free();
                    spin_lock();
                    t = timer->timer;
                    timer->timer = NULL;
                    spin_unlock();
                    hrtimer_cancel(&t->timer);
                    kfree(t);

/* UAF on t */
hrtimer_cancel(&t->timer);

In bpf_timer_cancel_and_free, this patch frees the timer->timer after a rcu grace period. This requires a rcu_head addition to the "struct bpf_hrtimer". Another kfree(t) happens in bpf_timer_init, this does not need a kfree_rcu because it is still under the spin_lock and timer->timer has not been visible by others yet.

In bpf_timer_cancel, rcu_read_lock() is added because this helper can be used in a non rcu critical section context (e.g. from a sleepable bpf prog). Other timer->timer usages in helpers.c have been audited, bpf_timer_cancel() is the only place where timer->timer is used outside of the spin_lock.

Another solution considered is to mark a t->flag in bpf_timer_cancel and clear it after hrtimer_cancel() is done. In bpf_timer_cancel_and_free, it busy waits for the flag to be cleared before kfree(t). This patch goes with a straight forward solution and frees timer->timer after a rcu grace period.

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{
  "affected": [],
  "aliases": [
    "CVE-2024-26737"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-04-03T17:15:51Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel\n\nThe following race is possible between bpf_timer_cancel_and_free\nand bpf_timer_cancel. It will lead a UAF on the timer-\u003etimer.\n\nbpf_timer_cancel();\n\tspin_lock();\n\tt = timer-\u003etime;\n\tspin_unlock();\n\n\t\t\t\t\tbpf_timer_cancel_and_free();\n\t\t\t\t\t\tspin_lock();\n\t\t\t\t\t\tt = timer-\u003etimer;\n\t\t\t\t\t\ttimer-\u003etimer = NULL;\n\t\t\t\t\t\tspin_unlock();\n\t\t\t\t\t\thrtimer_cancel(\u0026t-\u003etimer);\n\t\t\t\t\t\tkfree(t);\n\n\t/* UAF on t */\n\thrtimer_cancel(\u0026t-\u003etimer);\n\nIn bpf_timer_cancel_and_free, this patch frees the timer-\u003etimer\nafter a rcu grace period. This requires a rcu_head addition\nto the \"struct bpf_hrtimer\". Another kfree(t) happens in bpf_timer_init,\nthis does not need a kfree_rcu because it is still under the\nspin_lock and timer-\u003etimer has not been visible by others yet.\n\nIn bpf_timer_cancel, rcu_read_lock() is added because this helper\ncan be used in a non rcu critical section context (e.g. from\na sleepable bpf prog). Other timer-\u003etimer usages in helpers.c\nhave been audited, bpf_timer_cancel() is the only place where\ntimer-\u003etimer is used outside of the spin_lock.\n\nAnother solution considered is to mark a t-\u003eflag in bpf_timer_cancel\nand clear it after hrtimer_cancel() is done.  In bpf_timer_cancel_and_free,\nit busy waits for the flag to be cleared before kfree(t). This patch\ngoes with a straight forward solution and frees timer-\u003etimer after\na rcu grace period.",
  "id": "GHSA-8x8h-8p2w-8g4f",
  "modified": "2024-11-04T21:30:26Z",
  "published": "2024-04-03T18:30:42Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-26737"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0281b919e175bb9c3128bd3872ac2903e9436e3f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5268bb02107b9eedfdcd51db75b407d10043368c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7d80a9e745fa5b47da3bca001f186c02485c7c33"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8327ed12e8ebc5436bfaa1786c49988894f9c8a6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/addf5e297e6cbf5341f9c07720693ca9ba0057b5"
    }
  ],
  "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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