Re: [PATCH 4/5] perf sched: Cap max_cpu at MAX_CPUS in timehist sample processing

[David Ahern]

On 6/5/26 6:15 AM, Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> 
> perf_timehist__process_sample() updates sched->max_cpu from the
> sample CPU without bounds checking.  Later code uses max_cpu + 1 as
> an iteration count over arrays allocated with MAX_CPUS entries
> (curr_thread, cpu_last_switched).  A recording with CPU IDs >= MAX_CPUS
> causes out-of-bounds array accesses.
> 
> Also cap the env->nr_cpus_online initialization of max_cpu in
> perf_sched__timehist(), which could exceed MAX_CPUS on very large
> systems.
> 
> Add bounds checks before both max_cpu updates, matching the pattern
> already used in map_switch_event().
> 
> Fixes: 49394a2a24c7 ("perf sched timehist: Introduce timehist command")
> Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
> Cc: David Ahern <dsahern@xxxxxxxxx>
> Assisted-by: Claude Opus 4.6 <noreply@xxxxxxxxxxxxx>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> ---
>  tools/perf/builtin-sched.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 

LGTM

Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>