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Message-ID: <dce6ffbe-7580-db1a-dd24-798be27b3a26@alu.unizg.hr>
Date:   Thu, 30 Mar 2023 17:12:10 +0200
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Subject: Re: [BUG] [PATCH RFC v2] selftests/firmware: copious kernel memory
 leaks in test_fw_run_batch_request()
To:     Dan Carpenter <error27@gmail.com>,
        Luis Chamberlain <mcgrof@kernel.org>
Cc:     linux-kselftest@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Russ Weight <russell.h.weight@intel.com>,
        Takashi Iwai <tiwai@suse.de>,
        Tianfei zhang <tianfei.zhang@intel.com>,
        Shuah Khan <shuah@kernel.org>,
        Colin Ian King <colin.i.king@gmail.com>,
        Randy Dunlap <rdunlap@infradead.org>
References: <97e284be-5018-9d18-feb2-7ec4b08c06fd@alu.unizg.hr>
 <26fd581a-1b9f-4960-8457-61d725511cee@kili.mountain>
Content-Language: en-US, hr
From:   Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>
In-Reply-To: <26fd581a-1b9f-4960-8457-61d725511cee@kili.mountain>
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Precedence: bulk

Hi, all,

This is not a formal patch, but please see if you think the way the
locking and race are solved correctly this time.

(Having two mutexes over the same set of resources is obviously a hazard.)

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.

COMMENT: Like in libc putc() family of functions, there is also
putc_unlocked() The similar approach is applied here.

As the functions are callable from within both locked and non-locked
environment, we have to either:

1. have two or more locks, which is dubious in terms of concurrency
2. have locked and unlocked version of each function, for we cannot
    lock the same lock twice.

NOTE: Memory leaks are not solved with this patch, only a couple of
racing conditions.

---
diff --git a/lib/test_firmware.c b/lib/test_firmware.c
index 05ed84c2fc4c..d6ed20bd1eb0 100644
--- a/lib/test_firmware.c
+++ b/lib/test_firmware.c
@@ -353,6 +353,19 @@ static ssize_t config_test_show_str(char *dst,
         return len;
  }

+static inline int test_dev_config_update_bool_unlocked(const char *buf, size_t size,
+                                      bool *cfg)
+{
+       int ret;
+
+       if (kstrtobool(buf, cfg) < 0)
+               ret = -EINVAL;
+       else
+               ret = size;
+
+       return ret;
+}
+
  static int test_dev_config_update_bool(const char *buf, size_t size,
                                        bool *cfg)
  {
@@ -373,6 +386,24 @@ static ssize_t test_dev_config_show_bool(char *buf, bool val)
         return snprintf(buf, PAGE_SIZE, "%d\n", val);
  }

+static int test_dev_config_update_size_t_unlocked(
+                                        const char *buf,
+                                        size_t size,
+                                        size_t *cfg)
+{
+       int ret;
+       long new;
+
+       ret = kstrtol(buf, 10, &new);
+       if (ret)
+               return ret;
+
+       *(size_t *)cfg = new;
+
+       /* Always return full write size even if we didn't consume all */
+       return size;
+}
+
  static int test_dev_config_update_size_t(const char *buf,
                                          size_t size,
                                          size_t *cfg)
@@ -402,6 +433,21 @@ static ssize_t test_dev_config_show_int(char *buf, int val)
         return snprintf(buf, PAGE_SIZE, "%d\n", val);
  }

+static int test_dev_config_update_u8_unlocked(const char *buf, size_t size, u8 *cfg)
+{
+       u8 val;
+       int ret;
+
+       ret = kstrtou8(buf, 10, &val);
+       if (ret)
+               return ret;
+
+       *(u8 *)cfg = val;
+
+       /* Always return full write size even if we didn't consume all */
+       return size;
+}
+
  static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg)
  {
         u8 val;
@@ -471,10 +517,10 @@ 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);
+       rc = test_dev_config_update_u8_unlocked(buf, count,
+                                               &test_fw_config->num_requests);
+       mutex_unlock(&test_fw_mutex);

  out:
         return rc;
@@ -518,10 +564,10 @@ static ssize_t config_buf_size_store(struct device *dev,
                 mutex_unlock(&test_fw_mutex);
                 goto out;
         }
-       mutex_unlock(&test_fw_mutex);

-       rc = test_dev_config_update_size_t(buf, count,
-                                          &test_fw_config->buf_size);
+       rc = test_dev_config_update_size_t_unlocked(buf, count,
+                                                   &test_fw_config->buf_size);
+       mutex_unlock(&test_fw_mutex);

  out:
         return rc;
@@ -548,10 +594,10 @@ static ssize_t config_file_offset_store(struct device *dev,
                 mutex_unlock(&test_fw_mutex);
                 goto out;
         }
-       mutex_unlock(&test_fw_mutex);

-       rc = test_dev_config_update_size_t(buf, count,
-                                          &test_fw_config->file_offset);
+       rc = test_dev_config_update_size_t_unlocked(buf, count,
+                                                   &test_fw_config->file_offset);
+       mutex_unlock(&test_fw_mutex);

  out:
         return rc;

Best regards,
Mirsad

-- 
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?"