2022-04-26 14:56:27

by Colin Ian King

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

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 <[email protected]>
---

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);
fclose(fp);

--
2.35.1

2022-04-26 19:02:52

by Shuah Khan

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

On 4/26/22 6:25 AM, 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.
>
> 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 <[email protected]>
> ---
>
> 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);
> fclose(fp);
>
>

Thank you. Applied to linux-kselftest next for Linux 5.19-rc1

thanks,
-- Shuah