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

[Reinette Chatre]

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
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) {
-- 
2.46.0