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

[Ilpo Järvinen]

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@xxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxx>

-- 
 i.