Re: [RFC] perf session: Fix compression processing

[Jiri Olsa]

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?

jirka