Re: [PATCH 5/5] perf arm-spe: Reject zero nr_cpu in metadata to prevent division by zero

[Arnaldo Carvalho de Melo]

On Mon, Aug 03, 2026 at 09:46:49PM +0300, Adrian Hunter wrote:
> On 27/07/2026 19:17, Arnaldo Carvalho de Melo wrote:
> > From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > 
> > arm_spe__alloc_metadata() reads nr_cpu from the auxtrace_info priv
> > array without validation.  When a crafted perf.data provides nr_cpu=0,
> > the per_cpu_sz calculation divides by zero:
> > 
> >   per_cpu_sz = (metadata_size - (hdr_sz * sizeof(u64))) / (*nr_cpu);
> > 
> > Reject nr_cpu <= 0 early, before the division.  The caller already
> > treats NULL return with metadata_ver != 1 as a parse failure.
> > 
> > Fixes: e52abceb4b6c2723 ("perf arm-spe: Dump metadata with version 2")
> 
> git blame shows 7842a4b6ff698 "perf arm-spe: Support metadata version 2"
> for the relevant lines

That is right, Namhyung, can you please fix this Fixme tag while merging?

Thanks!

- Arnaldo
 
> > Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
> > Cc: Leo Yan <leo.yan@xxxxxxx>
> > Cc: James Clark <james.clark@xxxxxxxxxx>
> > Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> > Assisted-by: Claude:claude-opus-4.6
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > ---
> >  tools/perf/util/arm-spe.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
> > index 552f063f126e6769..401aab529309cbd6 100644
> > --- a/tools/perf/util/arm-spe.c
> > +++ b/tools/perf/util/arm-spe.c
> > @@ -1605,6 +1605,10 @@ static u64 **arm_spe__alloc_metadata(struct perf_record_auxtrace_info *info,
> >  	hdr_sz = ptr[ARM_SPE_HEADER_SIZE];
> >  	*nr_cpu = ptr[ARM_SPE_CPUS_NUM];
> >  
> > +	/* nr_cpu is used as a divisor below */
> > +	if (*nr_cpu <= 0)
> > +		return NULL;
> > +
> >  	metadata = calloc(*nr_cpu, sizeof(*metadata));
> >  	if (!metadata)
> >  		return NULL;