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

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On 4/24/22 3:15 PM, Colin Ian King wrote:
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.


How did you find this problem and how can it be reproduced? Is there
a case where test fails to open "/dev/null"?

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

thanks,
-- Shuah



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