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.
Fixes: a2561b12fe39 ("selftests/resctrl: Add built in benchmark")
Signed-off-by: Colin Ian King <[email protected]>
---
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
On 4/25/22 10:06 AM, Colin King (gmail) wrote:
> 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 :-)
>
I don't see how /dev/null open could fail here in this test.
However, I will take this fix. Please add information how
you found it and include the cppheck log in the commit log
and send me v2.
thanks,
-- Shuah
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 <[email protected]>
> ---
> 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
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 :-)
Colin
>
>> Fixes: a2561b12fe39 ("selftests/resctrl: Add built in benchmark")
>> Signed-off-by: Colin Ian King <[email protected]>
>> ---
>> 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