Re: [BUG] [PATCH RFC v1] selftests/firmware: copious kernel memory leaks in test_fw_run_batch_request()

[Mirsad Todorovac]

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

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