[PATCH AUTOSEL 6.6 14/16] selftests/resctrl: Protect against array overflow when reading strings

[Sasha Levin <sashal@kernel.org>]

From: Reinette Chatre <reinette.chatre@intel.com>

[ Upstream commit 46058430fc5d39c114f7e1b9c6ff14c9f41bd531 ]

resctrl selftests discover system properties via a variety of sysfs files.
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 contents of
/sys/bus/event_source/devices/uncore_imc_<imc instance>/events/cas_count_read
Similarly, the resctrl selftests discover the cache size via
/sys/bus/cpu/devices/cpu<id>/cache/index<index>/size.

Take care to do bounds checking when using fscanf() to read the
contents of files into a string buffer because by default fscanf() assumes
arbitrarily long strings. If the file contains more bytes than the array
can accommodate then an overflow will occur.

Provide a maximum field width to the conversion specifier to protect
against array overflow. The maximum is one less than the array size because
string input stores a terminating null byte that is not covered by the
maximum field width.

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>
---
 tools/testing/selftests/resctrl/resctrl_val.c | 4 ++--
 tools/testing/selftests/resctrl/resctrlfs.c   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
index 45439e726e79c..438dd86f2704c 100644
--- a/tools/testing/selftests/resctrl/resctrl_val.c
+++ b/tools/testing/selftests/resctrl/resctrl_val.c
@@ -179,7 +179,7 @@ static int read_from_imc_dir(char *imc_dir, int count)
 
 		return -1;
 	}
-	if (fscanf(fp, "%s", cas_count_cfg) <= 0) {
+	if (fscanf(fp, "%1023s", cas_count_cfg) <= 0) {
 		ksft_perror("Could not get iMC cas count read");
 		fclose(fp);
 
@@ -197,7 +197,7 @@ static int read_from_imc_dir(char *imc_dir, int count)
 
 		return -1;
 	}
-	if  (fscanf(fp, "%s", cas_count_cfg) <= 0) {
+	if  (fscanf(fp, "%1023s", cas_count_cfg) <= 0) {
 		ksft_perror("Could not get iMC cas count write");
 		fclose(fp);
 
diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 71ad2b335b83f..fe3241799841b 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -160,7 +160,7 @@ int get_cache_size(int cpu_no, char *cache_type, unsigned long *cache_size)
 
 		return -1;
 	}
-	if (fscanf(fp, "%s", cache_str) <= 0) {
+	if (fscanf(fp, "%63s", cache_str) <= 0) {
 		ksft_perror("Could not get cache_size");
 		fclose(fp);
 
-- 
2.43.0