[PATCH][V2] selftests/resctrl: Fix null pointer dereference on open failed

From: Colin Ian King
Date: Tue Apr 26 2022 - 08:25:42 EST

Currently if opening /dev/null fails to open then file pointer fp
is null and further access to fp via fprintf will cause a null
pointer dereference. Fix this by returning a negative error value
when a null fp is detected.

Detected using cppcheck static analysis:
tools/testing/selftests/resctrl/fill_buf.c:124:6: note: Assuming
that condition '!fp' is not redundant
if (!fp)
tools/testing/selftests/resctrl/fill_buf.c:126:10: note: Null
pointer dereference
fprintf(fp, "Sum: %d ", ret);

Fixes: a2561b12fe39 ("selftests/resctrl: Add built in benchmark")
Signed-off-by: Colin Ian King <colin.i.king@xxxxxxxxx>

V2: Add cppcheck analysis information

tools/testing/selftests/resctrl/fill_buf.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
index 51e5cf22632f..56ccbeae0638 100644
--- a/tools/testing/selftests/resctrl/fill_buf.c
+++ b/tools/testing/selftests/resctrl/fill_buf.c
@@ -121,8 +121,10 @@ static int fill_cache_read(unsigned char *start_ptr, unsigned char *end_ptr,

/* Consume read result so that reading memory is not optimized out. */
fp = fopen("/dev/null", "w");
- if (!fp)
+ if (!fp) {
perror("Unable to write to /dev/null");
+ return -1;
+ }
fprintf(fp, "Sum: %d ", ret);