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SubjectRe: [BUG] [PATCH RFC v1] selftests/firmware: copious kernel memory leaks in test_fw_run_batch_request()
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On 3/28/23 12:06, Dan Carpenter wrote:
> On Tue, Mar 28, 2023 at 11:23:00AM +0200, Mirsad Todorovac wrote:
>> The leaks are in chunks of 1024 bytes (+ overhead), but so far I could not
>> reproduce w/o root privileges, as tests refuse to run as unprivileged user.
>> (This is not the proof of non-existence of an unprivileged automated exploit
>> that would exhaust the kernel memory at approx. rate 4 MB/hour on our setup.
>>
>> This would mean about 96 MB / day or 3 GB / month (of kernel memory).
>
> This is firmware testing stuff. In the real world people aren't going
> to run their test scripts in a loop for days.
>
> There is no security implications. This is root only. Also if the
> user could load firmware then that would be the headline. Once someone
> is can already load firmware then who cares if they leak 100MB per day?
>
> It looks like if you call trigger_batched_requests_store() twice in a
> row then it will leak memory. Definitely test_fw_config->reqs is leaked.
> That's different from what the bug report is complaining about, but the
> point is that there are some obvious leaks. It looks like you're
> supposed to call trigger_batched_requests_store() in between runs?
>
> There are other races like config_num_requests_store() should hold the
> mutex over the call to test_dev_config_update_u8() instead of dropping
> and retaking it.

Hi Dan,

Following your insight and advice, I tried to mend this racing condition
like this:

diff --git a/lib/test_firmware.c b/lib/test_firmware.c
index 05ed84c2fc4c..6723c234ccbb 100644
--- a/lib/test_firmware.c
+++ b/lib/test_firmware.c
@@ -402,6 +402,8 @@ static ssize_t test_dev_config_show_int(char *buf, int val)
return snprintf(buf, PAGE_SIZE, "%d\n", val);
}

+static DEFINE_MUTEX(test_fw_mutex_update);
+
static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg)
{
u8 val;
@@ -411,9 +413,9 @@ static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg)
if (ret)
return ret;

- mutex_lock(&test_fw_mutex);
+ mutex_lock(&test_fw_mutex_update);
*(u8 *)cfg = val;
- mutex_unlock(&test_fw_mutex);
+ mutex_unlock(&test_fw_mutex_update);

/* Always return full write size even if we didn't consume all */
return size;
@@ -471,10 +473,10 @@ static ssize_t config_num_requests_store(struct device *dev,
mutex_unlock(&test_fw_mutex);
goto out;
}
- mutex_unlock(&test_fw_mutex);

rc = test_dev_config_update_u8(buf, count,
&test_fw_config->num_requests);
+ mutex_unlock(&test_fw_mutex);

out:
return rc;
For the second trigger_batched_requests_store(), probably the desired behaviour
would be to extend the list of test_fw_config->reqs, rather than destroying them
and allocating the new ones?

I am not certain about the desired semantics and where is it documented.

Thank you.

Best regards,

--
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia
"What’s this thing suddenly coming towards me very fast? Very very fast.
... I wonder if it will be friends with me?"

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