{ "schema_version": "1.6.1", "id": "RPI-CVE-2024-26737", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2024-26737" ], "published": "2024-04-03T17:31:22Z", "summary": "bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel", "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->timer.\n\nbpf_timer_cancel();\n\tspin_lock();\n\tt = timer->time;\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->timer;\n\t\t\t\t\t\ttimer->timer = NULL;\n\t\t\t\t\t\tspin_unlock();\n\t\t\t\t\t\thrtimer_cancel(&t->timer);\n\t\t\t\t\t\tkfree(t);\n\n\t/* UAF on t */\n\thrtimer_cancel(&t->timer);\n\nIn bpf_timer_cancel_and_free, this patch frees the timer->timer\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->timer 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->timer usages in helpers.c\nhave been audited, bpf_timer_cancel() is the only place where\ntimer->timer is used outside of the spin_lock.\n\nAnother solution considered is to mark a t->flag 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->timer after\na rcu grace period.", "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": [ "1:6.1.21-1+rpt1", "1:6.1.47-1+rpt2", "1:6.1.47-1+rpt4", "1:6.1.54-1+rpt2", "1:6.1.58-1+rpt2", "1:6.1.63-1+rpt1", "1:6.1.73-1+rpt1" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi1-rpi-v6", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi1-rpi-v7", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi1-rpi-v7l", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi1-rpi-v8", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi2-rpi-v6", "binary_version": "1:6.1.47-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi2-rpi-v7", "binary_version": "1:6.1.47-1+rpt2" 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rule)", "upstream_fixed": "6.1.80", "compiled_filter": false }, "1:6.1.54-1+rpt2": { "linux_commit": "2906f7abdc03d4a92b6b0e2e0c87ea2a9dffe8f7", "upstream_version": "6.1.54", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.80" }, "1:6.1.58-1+rpt2": { "linux_commit": "ccf1586ad0663fa91238ac56abf6340d6d740d18", "upstream_version": "6.1.58", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.80" }, "1:6.1.63-1+rpt1": { "linux_commit": null, "upstream_version": "6.1.63", "assessment": "upstream version (no usable Linux commit)", "upstream_fixed": "6.1.80" }, "1:6.1.73-1+rpt1": { "linux_commit": null, "upstream_version": "6.1.73", "assessment": "upstream version (no usable Linux commit)", "upstream_fixed": "6.1.80" } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2024-26737" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/5268bb02107b9eedfdcd51db75b407d10043368c" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/addf5e297e6cbf5341f9c07720693ca9ba0057b5" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/8327ed12e8ebc5436bfaa1786c49988894f9c8a6" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/7d80a9e745fa5b47da3bca001f186c02485c7c33" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/0281b919e175bb9c3128bd3872ac2903e9436e3f" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T11:52:36Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - Both sides of the race are driven through local syscalls \u2014 `bpf(BPF_PROG_LOAD)`/`BPF_PROG_TEST_RUN` to run a program calling `bpf_timer_cancel()`, and `BPF_MAP_DELETE_ELEM`/`close()` to drive `bpf_timer_cancel_and_free()`. No remotely supplied data reaches `kernel/bpf/helpers.c`, and BPF is classified as a local attack vector under kernel scoring guidance.\nAC:L - The attacker owns both racers \u2014 one thread runs its own BPF program calling `bpf_timer_cancel()` while another deletes the map element or drops the map uref \u2014 and can widen the window arbitrarily by making its own timer callback long-running, since `hrtimer_cancel()` blocks in `hrtimer_cancel_wait_running()` while the other thread finishes and `kfree()`s `t`. Nothing depends on state outside the attacker's control and the sequence can be retried in a tight loop.\nPR:L - The `bpf_timer_*` helpers are gated on `bpf_capable()` (CAP_BPF/CAP_SYS_ADMIN), a reduced non-root capability routinely delegated to unprivileged service, tracing and container workloads that are not init-namespace root. This matches this CNA's established scoring for the sibling `bpf_timer` UAFs CVE-2024-41045 and CVE-2024-42239.\nUI:N - The attacker loads its own program, arms its own timer, and issues both the cancel and the map-delete from its own threads. No victim action, mount, or interaction with any other principal is required.\nS:U - The freed `struct bpf_hrtimer` and the corrupted per-CPU hrtimer state are entirely kernel-internal, so the impact stays within the kernel's own security authority. No hypervisor, IOMMU, or sandbox boundary is crossed.\nC:H - `hrtimer_active()` reads `timer->base` out of the freed object and dereferences it (`base->seq`, `base->running`), so reclaiming the 96-byte `kmalloc-cg-96` slot with sprayed data (e.g. `msg_msg`) turns this into an attacker-directed kernel-memory read, with the helper's return value acting as an oracle. That yields arbitrary kernel data disclosure and KASLR defeat.\nI:H - After `hrtimer_active()` returns true, `lock_hrtimer_base()` takes a spinlock at an attacker-controlled address and `remove_hrtimer()`/`__remove_hrtimer()` writes `timer->state`, performs `timerqueue_del()` rb-tree unlinking and clears bits in `cpu_base->active_bases` through the same forged pointer. This is a controlled kernel write primitive suitable for privilege escalation.\nA:H - Even without a successful spray, operating on freed memory corrupts the per-CPU hrtimer queue and produces a KASAN splat, oops, or panic, and a garbage `timer->base` sends `hrtimer_cancel()` into an unterminating retry loop. The attacker can trigger this at will, repeatedly." } } }