From cad648cd7645697e955769642c3779a728b8987e Mon Sep 17 00:00:00 2001 From: Qing Ming Date: Sat, 16 May 2026 15:08:49 +0800 Subject: [PATCH] cgroup/rstat: validate cpu before css_rstat_cpu() access css_rstat_updated() is exposed as a BPF kfunc and accepts a caller-provided cpu argument. The function uses cpu for per-cpu rstat lookups without checking whether it refers to a valid possible CPU. A BPF iter/cgroup program with CAP_BPF and CAP_PERFMON can pass an invalid cpu value. On an unfixed UBSCAN_BOUNDS test kernel, cpu == 0x7fffffff triggers: UBSAN: array-index-out-of-bounds in kernel/cgroup/rstat.c:31:9 index 2147483647 is out of range for type 'long unsigned int [64]' Call Trace: css_rstat_updated bpf_iter_run_prog cgroup_iter_seq_show bpf_seq_read Add cpu validation to the BPF-facing css_rstat_updated() kfunc and move the common implementation to __css_rstat_updated() for in-kernel callers. Fixes: a319185be9f5 ("cgroup: bpf: enable bpf programs to integrate with rstat") Signed-off-by: Qing Ming --- block/blk-cgroup.c | 2 +- include/linux/cgroup.h | 1 + kernel/cgroup/rstat.c | 30 ++++++++++++++++++++---------- mm/memcontrol.c | 6 +++--- 4 files changed, 25 insertions(+), 14 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 554c87bb4a865..bc63bd220865d 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -2241,7 +2241,7 @@ void blk_cgroup_bio_start(struct bio *bio) } u64_stats_update_end_irqrestore(&bis->sync, flags); - css_rstat_updated(&blkcg->css, cpu); + __css_rstat_updated(&blkcg->css, cpu); put_cpu(); } diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index f6d037a30fd89..c5648fcf74e2e 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -777,6 +777,7 @@ static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen) /* * cgroup scalable recursive statistics. */ +void __css_rstat_updated(struct cgroup_subsys_state *css, int cpu); void css_rstat_updated(struct cgroup_subsys_state *css, int cpu); void css_rstat_flush(struct cgroup_subsys_state *css); diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index 150e5871e66f2..ed60ba119c687 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0-only #include "cgroup-internal.h" +#include #include #include @@ -53,7 +54,7 @@ static inline struct llist_head *ss_lhead_cpu(struct cgroup_subsys *ss, int cpu) } /** - * css_rstat_updated - keep track of updated rstat_cpu + * __css_rstat_updated - keep track of updated rstat_cpu * @css: target cgroup subsystem state * @cpu: cpu on which rstat_cpu was updated * @@ -63,20 +64,17 @@ static inline struct llist_head *ss_lhead_cpu(struct cgroup_subsys *ss, int cpu) * * NOTE: if the user needs the guarantee that the updater either add itself in * the lockless list or the concurrent flusher flushes its updated stats, a - * memory barrier is needed before the call to css_rstat_updated() i.e. a + * memory barrier is needed before the call to __css_rstat_updated() i.e. a * barrier after updating the per-cpu stats and before calling - * css_rstat_updated(). + * __css_rstat_updated(). */ -__bpf_kfunc void css_rstat_updated(struct cgroup_subsys_state *css, int cpu) +void __css_rstat_updated(struct cgroup_subsys_state *css, int cpu) { struct llist_head *lhead; struct css_rstat_cpu *rstatc; struct llist_node *self; - /* - * Since bpf programs can call this function, prevent access to - * uninitialized rstat pointers. - */ + /* Prevent access to uninitialized rstat pointers. */ if (!css_uses_rstat(css)) return; @@ -125,6 +123,18 @@ __bpf_kfunc void css_rstat_updated(struct cgroup_subsys_state *css, int cpu) llist_add(&rstatc->lnode, lhead); } +/* + * BPF-facing wrapper for __css_rstat_updated(). Validate the caller-provided + * CPU before passing it to the internal rstat updater. + */ +__bpf_kfunc void css_rstat_updated(struct cgroup_subsys_state *css, int cpu) +{ + if (unlikely(cpu < 0 || cpu >= nr_cpu_ids || !cpu_possible(cpu))) + return; + + __css_rstat_updated(css, cpu); +} + static void __css_process_update_tree(struct cgroup_subsys_state *css, int cpu) { /* put @css and all ancestors on the corresponding updated lists */ @@ -170,7 +180,7 @@ static void css_process_update_tree(struct cgroup_subsys *ss, int cpu) * flusher flush the stats updated by the updater who have * observed that they are already on the list. The * corresponding barrier pair for this one should be before - * css_rstat_updated() by the user. + * __css_rstat_updated() by the user. * * For now, there aren't any such user, so not adding the * barrier here but if such a use-case arise, please add @@ -614,7 +624,7 @@ static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp, unsigned long flags) { u64_stats_update_end_irqrestore(&rstatbc->bsync, flags); - css_rstat_updated(&cgrp->self, smp_processor_id()); + __css_rstat_updated(&cgrp->self, smp_processor_id()); put_cpu_ptr(rstatbc); } diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c03d4787d4668..749c128b4fad5 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -679,7 +679,7 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, long val, if (!val) return; - css_rstat_updated(&memcg->css, cpu); + __css_rstat_updated(&memcg->css, cpu); statc_pcpu = memcg->vmstats_percpu; for (; statc_pcpu; statc_pcpu = statc->parent_pcpu) { statc = this_cpu_ptr(statc_pcpu); @@ -2796,7 +2796,7 @@ static inline void account_slab_nmi_safe(struct mem_cgroup *memcg, struct mem_cgroup_per_node *pn = memcg->nodeinfo[pgdat->node_id]; /* preemption is disabled in_nmi(). */ - css_rstat_updated(&memcg->css, smp_processor_id()); + __css_rstat_updated(&memcg->css, smp_processor_id()); if (idx == NR_SLAB_RECLAIMABLE_B) atomic_add(nr, &pn->slab_reclaimable); else @@ -3019,7 +3019,7 @@ static inline void account_kmem_nmi_safe(struct mem_cgroup *memcg, int val) mod_memcg_state(memcg, MEMCG_KMEM, val); } else { /* preemption is disabled in_nmi(). */ - css_rstat_updated(&memcg->css, smp_processor_id()); + __css_rstat_updated(&memcg->css, smp_processor_id()); atomic_add(val, &memcg->kmem_stat); } }