linux-kernel - Re: [PATCH v1] perf session: fix decompression of PERF_RECORD

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Date:   Fri, 15 Nov 2019 16:11:24 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] perf session: fix decompression of
 PERF_RECORD_COMPRESSED records

On Fri, Nov 15, 2019 at 12:05:14PM +0300, Alexey Budankov wrote:
> 
> Avoid termination of trace loading in case the last record in 
> the decompressed buffer partly resides in the following 
> mmaped PERF_RECORD_COMPRESSED record. In this case NULL value
> returned by fetch_mmaped_event() means to proceed to the next 
> mmaped record then decompress it and load compressed events. 
> 
> The issue can be reproduced like this:
> 
>   $ perf record -z -- some_long_running_workload
>   $ 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
>   ...
> 
> Testing:
> 71: Zstd perf.data compression/decompression              : Ok
> 
> Fixes: 57fc032ad643 ("perf session: Avoid infinite loop when seeing invalid header.size")
> Link: https://marc.info/?l=linux-kernel&m=156580812427554&w=2
> Co-developed-by: Jiri Olsa <jolsa@...nel.org>
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
>  tools/perf/util/session.c | 47 +++++++++++++++++++++++++++++++++--------------
>  1 file changed, 33 insertions(+), 14 deletions(-)
> 
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index f07b8ecb91bc..3f6f812ec4ed 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1957,9 +1957,31 @@ static int __perf_session__process_pipe_events(struct perf_session *session)
>  	return err;
>  }
>  
> +static union perf_event *
> +prefetch_event(char *buf, u64 head, size_t mmap_size,
> +	       bool needs_swap, union perf_event *ret);

why not move prefetch_event definition in here?
I don't see any need for the static declaration..

> +
>  static union perf_event *
>  fetch_mmaped_event(struct perf_session *session,
>  		   u64 head, size_t mmap_size, char *buf)
> +{
> +	return prefetch_event(buf, head, mmap_size,
> +			      session->header.needs_swap,
> +			      ERR_PTR(-EINVAL));
> +}
> +
> +static union perf_event *
> +fetch_decomp_event(struct perf_session *session,
> +		   u64 head, size_t mmap_size, char *buf)
> +{

if this is decomp specific, it could take 'struct decomp*' as argument

> +	return prefetch_event(buf, head, mmap_size,
> +			      session->header.needs_swap,
> +			      NULL);
> +}
> +
> +static union perf_event *
> +prefetch_event(char *buf, u64 head, size_t mmap_size,
> +	       bool needs_swap, union perf_event *ret)
>  {

'error' might be more suitable then ret in here

thanks,
jirka