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SubjectRe: [PATCH] perf record: Fix segmentation fault in record__read_lost_samples()
Hi Leo,

On Sat, Sep 24, 2022 at 4:34 AM Leo Yan <leo.yan@linaro.org> wrote:
>
> Commit a49aa8a54e86 ("perf record: Read and inject LOST_SAMPLES events")
> causes segmentation fault when run the "perf mem record" command in
> unprivileged mode, the output log is:
>
> $ ./perf mem record --all-user -o perf_test.data -- ./test_program
> Error:
> Access to performance monitoring and observability operations is limited.
> Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open
> access to performance monitoring and observability operations for processes
> without CAP_PERFMON, CAP_SYS_PTRACE or CAP_SYS_ADMIN Linux capability.
> More information can be found at 'Perf events and tool security' document:
> https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html
> perf_event_paranoid setting is 4:
> -1: Allow use of (almost) all events by all users
> Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
> >= 0: Disallow raw and ftrace function tracepoint access
> >= 1: Disallow CPU event access
> >= 2: Disallow kernel profiling
> To make the adjusted perf_event_paranoid setting permanent preserve it
> in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)
> perf: Segmentation fault
> Obtained 16 stack frames.
> ./perf(dump_stack+0x31) [0x55b7aa1e8070]
> ./perf(sighandler_dump_stack+0x36) [0x55b7aa1e815e]
> ./perf(+0xc9120) [0x55b7aa0a9120]
> /lib/x86_64-linux-gnu/libc.so.6(+0x4251f) [0x7fd03ef8151f]
> ./perf(+0xccaca) [0x55b7aa0acaca]
> ./perf(+0xcf4ab) [0x55b7aa0af4ab]
> ./perf(cmd_record+0xd50) [0x55b7aa0b28df]
> ./perf(+0x112f77) [0x55b7aa0f2f77]
> ./perf(cmd_mem+0x53b) [0x55b7aa0f406c]
> ./perf(+0x19979c) [0x55b7aa17979c]
> ./perf(+0x199a37) [0x55b7aa179a37]
> ./perf(+0x199b95) [0x55b7aa179b95]
> ./perf(main+0x2c7) [0x55b7aa179fbd]
> /lib/x86_64-linux-gnu/libc.so.6(+0x29d8f) [0x7fd03ef68d8f]
> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x7f) [0x7fd03ef68e3f]
> ./perf(_start+0x24) [0x55b7aa089974]
> Segmentation fault (core dumped)
>
> In the unprivileged mode perf fails to open PMU event, the function
> record__open() returns error and "session->evlist" is NULL; this leads
> to segmentation fault when iterates "session->evlist" in the function
> record__read_lost_samples().
>
> This patch checks "session->evlist" in record__read_lost_samples(), if
> "session->evlist" is NULL then the function directly bails out to avoid
> segmentation fault.
>
> Fixes: a49aa8a54e86 ("perf record: Read and inject LOST_SAMPLES events")
> Signed-off-by: Leo Yan <leo.yan@linaro.org>

Thanks for the fix and sorry for the inconvenience.
Actually I sent the same fix a few weeks ago.

https://lore.kernel.org/r/20220909235024.278281-1-namhyung@kernel.org

Thanks,
Namhyung


> ---
> tools/perf/builtin-record.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 02e38f50a138..012b46dd4999 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1888,6 +1888,10 @@ static void record__read_lost_samples(struct record *rec)
> struct perf_record_lost_samples *lost;
> struct evsel *evsel;
>
> + /* No any event is opened, directly bail out */
> + if (!session->evlist)
> + return;
> +
> lost = zalloc(PERF_SAMPLE_MAX_SIZE);
> if (lost == NULL) {
> pr_debug("Memory allocation failed\n");
> --
> 2.34.1
>

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