selftests/resctrl: Protect against array overrun during iMC config parsing

[ Upstream commit 48ed4e79 ]

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.
Remove the unnecessary append of a delimiter to the string 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: 1d3f0868 ("selftests/resctrl: Read memory bandwidth from perf IMC counter and from resctrl file system")
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>