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

Ilpo Järvinen
2024-09-30T13:35:34Z

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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.

> 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>

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i.