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SubjectRe: [PATCH V6 05/12] perf tools: tidy up sample parsing overflow checking
On Tue, Jul 16, 2013 at 09:38:11AM +0300, Adrian Hunter wrote:
> The size of data retrieved from a sample event must be
> validated to ensure it does not go past the end of the
> event. That was being done sporadically and without
> considering integer overflows.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> ---
> tools/perf/util/evsel.c | 102 ++++++++++++++++++++++++++++++------------------
> 1 file changed, 64 insertions(+), 38 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 724b75a..20e2ed9 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1114,24 +1114,38 @@ static int perf_evsel__parse_id_sample(const struct perf_evsel *evsel,
> return 0;
> }
>
> -static bool sample_overlap(const union perf_event *event,
> - const void *offset, u64 size)
> +static inline bool overflow_one(const void *endp, const void *offset)
> {
> - const void *base = event;
> -
> - if (offset + size > base + event->header.size)
> - return true;
> + return offset + sizeof(u64) > endp;
> +}
>
> - return false;
> +static inline bool overflow(const void *endp, u16 max_size, const void *offset,
> + u64 size)
> +{
> + return size > max_size || offset + size > endp;

hum, does '(size > max_size)' catch anything that would
not be catched by '(offset + size > endp)' ?

> }
>
> +#define OVERFLOW_CHECK_ONE(offset) \
> + do { \
> + if (overflow_one(endp, (offset))) \
> + return -EFAULT; \
> + } while (0)
> +
> +#define OVERFLOW_CHECK(offset, size) \
> + do { \
> + if (overflow(endp, max_size, (offset), (size))) \
> + return -EFAULT; \
> + } while (0)

I think, it'd be better to have just one overflow check function, like:

static inline bool overflow(const void *endp, const void *offset, u64 size)
{
return offset + size > endp;
}

#define OVERFLOW_CHECK(offset, size) \
do { \
if (overflow(endp, (offset), (size))) \
return -EFAULT; \
} while (0)

#define OVERFLOW_CHECK_u64(offset) OVERFLOW_CHECK(offset, sizeof(u64))

> +
> int perf_evsel__parse_sample(struct perf_evsel *evsel, union perf_event *event,
> struct perf_sample *data)
> {

Hum, I was thinking of making this check more general and
cover also perf_event__synthesize_sample function.. but
looks like it's not needed there..?


> u64 type = evsel->attr.sample_type;
> - u64 regs_user = evsel->attr.sample_regs_user;
> bool swapped = evsel->needs_swap;
> const u64 *array;
> + u16 max_size = event->header.size;
> + const void *endp = (void *)event + max_size;
> + u64 sz;
>
> /*
> * used for cross-endian analysis. See git commit 65014ab3
> @@ -1153,6 +1167,11 @@ int perf_evsel__parse_sample(struct perf_evsel *evsel, union perf_event *event,
>
> array = event->sample.array;
>
> + /*
> + * sample_size is based on PERF_SAMPLE_MASK which includes up to

please prepend ^^^: The evsel's

> + * PERF_SAMPLE_PERIOD. After that overflow_one() or overflow() must be
> + * used to check the format does not go past the end of the event.
> + */
> if (evsel->sample_size + sizeof(event->header) > event->header.size)
> return -EFAULT;
>

thanks,
jirka


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