Re: [RFC] perf session: Fix compression processing

[Alexey Budankov]

On 11.11.2019 17:56, Jiri Olsa wrote:
> On Mon, Nov 11, 2019 at 05:38:49PM +0300, Alexey Budankov wrote:
>>
>> On 04.11.2019 1:24, Jiri Olsa wrote:
>>> hi,
>> <SNIP>
>>> ---
>>> The compressed data processing occasionally fails with:
>>>   $ perf report --stdio -vv
>>>   decomp (B): 44519 to 163000
>>>   decomp (B): 48119 to 174800
>>>   decomp (B): 65527 to 131072
>>>   fetch_mmaped_event: head=0x1ffe0 event->header_size=0x28, mmap_size=0x20000: fuzzed perf.data?
>>>   Error:
>>>   failed to process sample
>>>   ...
>>>
>>> It's caused by recent fuzzer fix that does not take into account
>>> that compressed data do not need to by fully present in the buffer,
>>> so it's ok to just return NULL and not to fail.
>>>
>>> Fixes: 57fc032ad643 ("perf session: Avoid infinite loop when seeing invalid header.size")
>>> Link: http://lkml.kernel.org/n/tip-q1biqscs4stcmc9bs1iokfro@xxxxxxxxxxxxxx
>>> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
>>> ---
>>>  tools/perf/util/session.c | 8 +++++---
>>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
>>> index f07b8ecb91bc..3589ed14a629 100644
>>> --- a/tools/perf/util/session.c
>>> +++ b/tools/perf/util/session.c
>>> @@ -1959,7 +1959,7 @@ static int __perf_session__process_pipe_events(struct perf_session *session)
>>>  
>>>  static union perf_event *
>>>  fetch_mmaped_event(struct perf_session *session,
>>> -		   u64 head, size_t mmap_size, char *buf)
>>> +		   u64 head, size_t mmap_size, char *buf, bool decomp)
>>
>> bools in interface make code less transparent.
>>
>>>  {
>>>  	union perf_event *event;
>>>  
>>> @@ -1979,6 +1979,8 @@ fetch_mmaped_event(struct perf_session *session,
>>>  		/* We're not fetching the event so swap back again */
>>>  		if (session->header.needs_swap)
>>>  			perf_event_header__bswap(&event->header);
>>> +		if (decomp)
>>> +			return NULL;
>>>  		pr_debug("%s: head=%#" PRIx64 " event->header_size=%#x, mmap_size=%#zx: fuzzed perf.data?\n",
>>>  			 __func__, head, event->header.size, mmap_size);
>>>  		return ERR_PTR(-EINVAL);
>>> @@ -1997,7 +1999,7 @@ static int __perf_session__process_decomp_events(struct perf_session *session)
>>>  		return 0;
>>>  
>>>  	while (decomp->head < decomp->size && !session_done()) {
>>> -		union perf_event *event = fetch_mmaped_event(session, decomp->head, decomp->size, decomp->data);
>>> +		union perf_event *event = fetch_mmaped_event(session, decomp->head, decomp->size, decomp->data, true);
>>
>> It looks like this call can be skipped, at all, in this case.
> 
> not sure what you mean, we are in decomp code no?

Ok, it is inside "not fetching" branch. 
NULL return value means to proceed getting further over the trace.
Checking record type == COMPRESSED at the higher level could 
probably be cleaner fix and also work faster.

~Alexey

> 
> jirka
> 
>