Re: [PATCH] perf: prevent overflow in size calculation

[Namhyung Kim <namhyung@kernel.org>]

Hi, Cody

On Thu, 19 Jul 2012 17:13:35 -0700, Cody Schafer wrote:
> A large enough symbol size causes an overflow in the size parameter to the
> histogram allocation, leading to a segfault in symbol__inc_addr_samples later
> on when this histogram is accessed.
>
> In the case of being called via perf-report, this returns back and
> gracefully ignores the sample, eventually ignoring the chained return
> value of perf_session_deliver_event in flush_sample_queue.
>
> Signed-off-by: Cody Schafer <cody@linux.vnet.ibm.com>
> ---
>  tools/perf/util/annotate.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> index 8069dfb..6f78f20 100644
> --- a/tools/perf/util/annotate.c
> +++ b/tools/perf/util/annotate.c
> @@ -426,8 +426,13 @@ int symbol__alloc_hist(struct symbol *sym)
>  {
>  	struct annotation *notes = symbol__annotation(sym);
>  	const size_t size = symbol__size(sym);
> -	size_t sizeof_sym_hist = (sizeof(struct sym_hist) + size * sizeof(u64));
> +	size_t sizeof_sym_hist;
>  
> +	/* Check for overflow when calculating sizeof_sym_hist */
> +	if (size > (SIZE_MAX / sizeof(u64)))
> +		return -1;

How does it guarantee that the end result which used in zalloc below
would not overflow?

Thanks,
Namhyung


> +
> +	sizeof_sym_hist = (sizeof(struct sym_hist) + size * sizeof(u64));
>  	notes->src = zalloc(sizeof(*notes->src) + symbol_conf.nr_events * sizeof_sym_hist);
>  	if (notes->src == NULL)
>  		return -1;