linux-kernel - Re: [PATCH v3] perf session: fix decompression of PERF_RECORD

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Date:   Tue, 19 Nov 2019 21:05:10 +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>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] perf session: fix decompression of
 PERF_RECORD_COMPRESSED records

On Mon, Nov 18, 2019 at 05:21:03PM +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
> 
>   $ tools/perf/perf report -vv --stdio
>   decomp (B): 59593 to 262160
>   decomp (B): 4438 to 16512
>   decomp (B): 285 to 880
>   Looking at the vmlinux_path (8 entries long)
>   Using vmlinux for symbols
>   decomp (B): 57474 to 261248
>   prefetch_event: head=0x3fc78 event->header_size=0x28, mmap_size=0x3fc80: fuzzed or compressed perf.data?
>   decomp (B): 25 to 32
>   decomp (B): 52 to 120
>   ...
> 
> 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>

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka