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

From: Colin King (gmail)
Date: Mon Apr 25 2022 - 12:06:29 EST

On 25/04/2022 16:51, Shuah Khan wrote:
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"?

Found with static analysis, cppcheck. Open on /dev/null is unlikely to fail, but it's good to fail reliably rather than have a SIGSEGV :-)


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);

-- Shuah