[PATCH] perf jevents: Fix segfault in perf_pmu__find_events_table

[PATCH] perf jevents: Fix segfault in perf_pmu__find_events_table

[Yang Jihong]

Before caching the JSON events table, perf_pmu__find_events_table() need
to check whether table is empty.

For example, AuthenticAMD-15-6B-1 is used. The matching events table cannot
be found. As a result, a null pointer is accessed when caching JSON events
table, causing segfault.

Before:
  # perf record -vv true
  DEBUGINFOD_URLS=
  Using CPUID AuthenticAMD-15-6B-1
  Segmentation fault (core dumped)

After:
  # perf record -vv true
  DEBUGINFOD_URLS=
  Using CPUID AuthenticAMD-15-6B-1
  <SNIP>
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.005 MB perf.data ]

Fixes: 7c52f10c0d4d ("perf pmu: Cache JSON events table")
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
---
 tools/perf/pmu-events/jevents.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
index a7e88332276d..72ba4a9239c6 100755
--- a/tools/perf/pmu-events/jevents.py
+++ b/tools/perf/pmu-events/jevents.py
@@ -991,7 +991,7 @@ const struct pmu_events_table *perf_pmu__find_events_table(struct perf_pmu *pmu)
                 }
         }
         free(cpuid);
-        if (!pmu)
+        if (!pmu || !table)
                 return table;
 
         for (i = 0; i < table->num_pmus; i++) {
-- 
2.34.1

Re: [PATCH] perf jevents: Fix segfault in perf_pmu__find_events_table

[Namhyung Kim]

Hello,

On Sun, Sep 17, 2023 at 8:05 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>
> Before caching the JSON events table, perf_pmu__find_events_table() need
> to check whether table is empty.
>
> For example, AuthenticAMD-15-6B-1 is used. The matching events table cannot
> be found. As a result, a null pointer is accessed when caching JSON events
> table, causing segfault.
>
> Before:
>   # perf record -vv true
>   DEBUGINFOD_URLS=
>   Using CPUID AuthenticAMD-15-6B-1
>   Segmentation fault (core dumped)
>
> After:
>   # perf record -vv true
>   DEBUGINFOD_URLS=
>   Using CPUID AuthenticAMD-15-6B-1
>   <SNIP>
>   [ perf record: Woken up 1 times to write data ]
>   [ perf record: Captured and wrote 0.005 MB perf.data ]
>
> Fixes: 7c52f10c0d4d ("perf pmu: Cache JSON events table")
> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>

Thanks for the fix but please see

https://lore.kernel.org/all/20230913125157.2790375-1-tmricht@linux.ibm.com/

Thanks,
Namhyung


> ---
>  tools/perf/pmu-events/jevents.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
> index a7e88332276d..72ba4a9239c6 100755
> --- a/tools/perf/pmu-events/jevents.py
> +++ b/tools/perf/pmu-events/jevents.py
> @@ -991,7 +991,7 @@ const struct pmu_events_table *perf_pmu__find_events_table(struct perf_pmu *pmu)
>                  }
>          }
>          free(cpuid);
> -        if (!pmu)
> +        if (!pmu || !table)
>                  return table;
>
>          for (i = 0; i < table->num_pmus; i++) {
> --
> 2.34.1
>

Re: [PATCH] perf jevents: Fix segfault in perf_pmu__find_events_table

[Yang Jihong]

Hello,

On 2023/9/19 7:55, Namhyung Kim wrote:
> Hello,
> 
> On Sun, Sep 17, 2023 at 8:05 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>>
>> Before caching the JSON events table, perf_pmu__find_events_table() need
>> to check whether table is empty.
>>
>> For example, AuthenticAMD-15-6B-1 is used. The matching events table cannot
>> be found. As a result, a null pointer is accessed when caching JSON events
>> table, causing segfault.
>>
>> Before:
>>    # perf record -vv true
>>    DEBUGINFOD_URLS=
>>    Using CPUID AuthenticAMD-15-6B-1
>>    Segmentation fault (core dumped)
>>
>> After:
>>    # perf record -vv true
>>    DEBUGINFOD_URLS=
>>    Using CPUID AuthenticAMD-15-6B-1
>>    <SNIP>
>>    [ perf record: Woken up 1 times to write data ]
>>    [ perf record: Captured and wrote 0.005 MB perf.data ]
>>
>> Fixes: 7c52f10c0d4d ("perf pmu: Cache JSON events table")
>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> 
> Thanks for the fix but please see
> 
> https://lore.kernel.org/all/20230913125157.2790375-1-tmricht@linux.ibm.com/
> 

Uh.. no notice that there is already a fix, please ignore it.

Thanks,
Yang