Re: [PATCH V2 04/13] selftests/resctrl: Protect against array overrun during iMC config parsing

Reinette Chatre
2024-09-30T16:04:13Z

Hi Ilpo,

On 9/30/24 6:35 AM, Ilpo Järvinen wrote:
> On Thu, 12 Sep 2024, Reinette Chatre wrote:
>
>> The MBM and MBA tests need to discover the event and umask with which to
>> configure the performance event used to measure read memory bandwidth.
>> This is done by parsing the
>> /sys/bus/event_source/devices/uncore_imc_<imc instance>/events/cas_count_read
>> file for each iMC instance that contains the formatted
>> output: "event=<event>,umask=<umask>"
>>
>> Parsing of cas_count_read contents is done by initializing an array of
>> MAX_TOKENS elements with tokens (deliminated by "=,") from this file.
>> Start by removing the unnecessary append of a delimiter to the string
>
> Start what? (It sounds odd given the lack of any context, my guess is
> you're trying to refer to start/first one of the changes you make in the
> patch but the textual context does not support that conclusion.) I suggest
> you just rephrase it and avoid using "start" word altogether.

Indeed, I'll just drop the "Start by" and have the sentence be:
"Remove the unnecessary append of a delimiter ..."

>
>> needing to be parsed. Per the strtok() man page: "delimiter bytes at
>> the start or end of the string are ignored". This has no impact on
>> the token placement within the array.
>>
>> After initialization, the actual event and umask is determined by
>> parsing the tokens directly following the "event" and "umask" tokens
>> respectively.
>>
>> Iterating through the array up to index "i < MAX_TOKENS" but then
>> accessing index "i + 1" risks array overrun during the final iteration.
>> Avoid array overrun by ensuring that the index used within for
>> loop will always be valid.
>>
>> Fixes: 1d3f08687d76 ("selftests/resctrl: Read memory bandwidth from perf IMC counter and from resctrl file system")
>> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
>> ---
>> Changes since V1:
>> - New patch.
>> ---
>> tools/testing/selftests/resctrl/resctrl_val.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
>> index 70e8e31f5d1a..e88d5ca30517 100644
>> --- a/tools/testing/selftests/resctrl/resctrl_val.c
>> +++ b/tools/testing/selftests/resctrl/resctrl_val.c
>> @@ -83,13 +83,12 @@ static void get_event_and_umask(char *cas_count_cfg, int count, bool op)
>> char *token[MAX_TOKENS];
>> int i = 0;
>>
>> - strcat(cas_count_cfg, ",");
>> token[0] = strtok(cas_count_cfg, "=,");
>>
>> for (i = 1; i < MAX_TOKENS; i++)
>> token[i] = strtok(NULL, "=,");
>>
>> - for (i = 0; i < MAX_TOKENS; i++) {
>> + for (i = 0; i < MAX_TOKENS - 1; i++) {
>> if (!token[i])
>> break;
>> if (strcmp(token[i], "event") == 0) {
>>
>
> The code change seems fine so after improving the commit message, please
> add:
>
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
>

Thank you very much.

Reinette