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cgroup: Fixes for v7.1-rc4

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Two rstat fixes:
 
 - Out-of-bounds access in the css_rstat_updated() BPF kfunc when called
   with an unchecked user-supplied cpu.
 
 - Over-strict NMI guard after the recent switch to try_cmpxchg left
   sparc and ppc64 unable to queue rstat updates from NMI.
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Merge tag 'cgroup-for-7.1-rc4-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

Pull cgroup fixes from Tejun Heo:
 "Two rstat fixes:

   - Out-of-bounds access in the css_rstat_updated() BPF kfunc when
     called with an unchecked user-supplied cpu

   - Over-strict NMI guard after the recent switch to try_cmpxchg left
     sparc and ppc64 unable to queue rstat updates from NMI"

* tag 'cgroup-for-7.1-rc4-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: rstat: relax NMI guard after switch to try_cmpxchg
  cgroup/rstat: validate cpu before css_rstat_cpu() access
This commit is contained in:
Linus Torvalds 2026-05-22 16:28:47 -07:00
commit de37e502a3
4 changed files with 28 additions and 18 deletions
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2
block/blk-cgroup.c
View File

@ -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();
}

1
include/linux/cgroup.h
View File

@ -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);

37
kernel/cgroup/rstat.c
View File

@ -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
*
@ -63,31 +64,27 @@ 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;
lockdep_assert_preemption_disabled();
/*
* For archs withnot nmi safe cmpxchg or percpu ops support, ignore
* the requests from nmi context.
* The lockless insertion below relies on NMI-safe cmpxchg;
* bail out in NMI on archs that don't provide it.
*/
if ((!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) ||
!IS_ENABLED(CONFIG_ARCH_HAS_NMI_SAFE_THIS_CPU_OPS)) && in_nmi())
if (!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) && in_nmi())
return;
rstatc = css_rstat_cpu(css, cpu);
@ -125,6 +122,18 @@ __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 +179,7 @@ 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 +623,7 @@ 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);
}

6
mm/memcontrol.c
View File

@ -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);
}
}