Re: [RFC] perf session: Fix compression processing

[Alexey Budankov]

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.

>  
>  		if (IS_ERR(event))
>  			return PTR_ERR(event);
> @@ -2100,7 +2102,7 @@ reader__process_events(struct reader *rd, struct perf_session *session,
>  	}
>  
>  more:
> -	event = fetch_mmaped_event(session, head, mmap_size, buf);
> +	event = fetch_mmaped_event(session, head, mmap_size, buf, false);
>  	if (IS_ERR(event))
>  		return PTR_ERR(event);
>  
> 

~Alexey