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SubjectRe: [PATCH V6 05/12] perf tools: tidy up sample parsing overflow checking
On 16/07/13 14:53, Jiri Olsa wrote:
> 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)' ?

'offset + size' can overflow and end up less than 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))
>

OK

>> +
>> 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..?

Currently the caller must ensure there is enough space.

>
>
>> 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

OK

>
>> + * 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;
>>



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