Re: [PATCH 4.14] perf machine: Guard against NULL in machine__exit()

[Greg KH]

On Wed, Jun 19, 2019 at 12:00:46PM +0000, Rantala, Tommi T. (Nokia - FI/Espoo) wrote:
> From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> 
> commit 4a2233b194c77ae1ea8304cb7c00b551de4313f0 upstream.
> 
> A recent fix for 'perf trace' introduced a bug where
> machine__exit(trace->host) could be called while trace->host was still
> NULL, so make this more robust by guarding against NULL, just like
> free() does.
> 
> The problem happens, for instance, when !root users try to run 'perf
> trace':
> 
>   [acme@jouet linux]$ trace
>   Error:	No permissions to read /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
>   Hint:	Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'
> 
>   perf: Segmentation fault
>   Obtained 7 stack frames.
>   [0x4f1b2e]
>   /lib64/libc.so.6(+0x3671f) [0x7f43a1dd971f]
>   [0x4f3fec]
>   [0x47468b]
>   [0x42a2db]
>   /lib64/libc.so.6(__libc_start_main+0xe9) [0x7f43a1dc3509]
>   [0x42a6c9]
>   Segmentation fault (core dumped)
>   [acme@jouet linux]$
> 
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Andrei Vagin <avagin@xxxxxxxxxx>
> Cc: David Ahern <dsahern@xxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Vasily Averin <vvs@xxxxxxxxxxxxx>
> Cc: Wang Nan <wangnan0@xxxxxxxxxx>
> Fixes: 33974a414ce2 ("perf trace: Call machine__exit() at exit")
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Signed-off-by: Tommi Rantala <tommi.t.rantala@xxxxxxxxx>
> ---
>  tools/perf/util/machine.c | 3 +++
>  1 file changed, 3 insertions(+)

Now applied, thanks.

greg k-h