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 <a0yami@mailbox.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 554c87bb4a8651daae006cc039006a0539d6894b..bc63bd220865dc91f10e394242ee3969e64f17d4 100644 (file)
--- 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 e52160e85af4b5ba8b3540733aca20a2250fffee..e011dc43fcf14b33f16af4001067eba3410934b1 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -776,6 +776,7 @@ 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 150e5871e66f255b7aef4e1adf1e7a59fb09dc06..ed60ba119c687b6dfeab3f45063880ce7f78a707 100644 (file)
--- 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 <linux/cpumask.h>
 #include <linux/sched/cputime.h>
 
 #include <linux/bpf.h>
@@ -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 051b82ebf371c3cd494534dac30dc0683b9a3a8e..c7e60f26013c14d167ac9c59a2d67b7b912a5708 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -579,7 +579,7 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int 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);
@@ -2608,7 +2608,7 @@ 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
@@ -2832,7 +2832,7 @@ 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);
        }
 }