linux-kernel - Re: [PATCH] btrfs: Fix a memory leak in btrfs_ioctl

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Message-ID: <e876305b-5497-22bd-e0d1-bfd8d9289ff0@gmx.com>
Date:   Thu, 21 Apr 2022 19:41:15 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Nikolay Borisov <nborisov@...e.com>,
        Haowen Bai <baihaowen@...zu.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: Fix a memory leak in btrfs_ioctl_balance()



On 2022/4/21 19:25, Nikolay Borisov wrote:
> 
> 
> On 21.04.22 г. 14:21 ч., Nikolay Borisov wrote:
>>
>>
>> On 21.04.22 г. 12:51 ч., Haowen Bai wrote:
>>> Free "bargs" before return.
>>>
>>> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
>>> ---
>>>   fs/btrfs/ioctl.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>>> index f08233c2b0b2..d4c8bea914b7 100644
>>> --- a/fs/btrfs/ioctl.c
>>> +++ b/fs/btrfs/ioctl.c
>>> @@ -4389,13 +4389,13 @@ static long btrfs_ioctl_balance(struct file 
>>> *file, void __user *arg)
>>>               /* this is (2) */
>>>               mutex_unlock(&fs_info->balance_mutex);
>>>               ret = -EINPROGRESS;
>>> -            goto out;
>>> +            goto out_bargs;
>>>           }
>>>       } else {
>>>           /* this is (1) */
>>>           mutex_unlock(&fs_info->balance_mutex);
>>>           ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
>>> -        goto out;
>>> +        goto out_bargs;
>>>       }
>>>   locked:
>>
>> I think this is a better fix:
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index 7a6974e877f4..906ed1b93654 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -4391,15 +4391,13 @@ static long btrfs_ioctl_balance(struct file 
>> *file, void __user *arg)
>>                          goto again;
>>                  } else {
>>                          /* this is (2) */
>> -                       mutex_unlock(&fs_info->balance_mutex);
>>                          ret = -EINPROGRESS;
>> -                       goto out;
>> +                       goto out_bargs;
>>                  }
>>          } else {
>>                  /* this is (1) */
>> -               mutex_unlock(&fs_info->balance_mutex);
>>                  ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
>> -               goto out;
>> +               goto out_bargs;
>>          }
>>
>>   locked:
>>
> 
> 
> Actually to simplify further:
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 7a6974e877f4..bbda55d41a06 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -4353,6 +4353,7 @@ static long btrfs_ioctl_balance(struct file *file, 
> void __user *arg)
>          bargs = memdup_user(arg, sizeof(*bargs));
>          if (IS_ERR(bargs)) {
>                  ret = PTR_ERR(bargs);
> +               bargs = NULL;
>                  goto out;
>          }
> 
> @@ -4391,13 +4392,11 @@ static long btrfs_ioctl_balance(struct file 
> *file, void __user *arg)
>                          goto again;
>                  } else {
>                          /* this is (2) */
> -                       mutex_unlock(&fs_info->balance_mutex);
>                          ret = -EINPROGRESS;
>                          goto out;
>                  }
>          } else {
>                  /* this is (1) */
> -               mutex_unlock(&fs_info->balance_mutex);
>                  ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
>                  goto out;
>          }
> @@ -4406,7 +4405,7 @@ static long btrfs_ioctl_balance(struct file *file, 
> void __user *arg)
>          if (bargs->flags & BTRFS_BALANCE_RESUME) {
>                  if (!fs_info->balance_ctl) {
>                          ret = -ENOTCONN;
> -                       goto out_bargs;
> +                       goto out;
>                  }
> 
>                  bctl = fs_info->balance_ctl;
> @@ -4420,18 +4419,18 @@ static long btrfs_ioctl_balance(struct file 
> *file, void __user *arg)
> 
>          if (bargs->flags & ~(BTRFS_BALANCE_ARGS_MASK | 
> BTRFS_BALANCE_TYPE_MASK)) {
>                  ret = -EINVAL;
> -               goto out_bargs;
> +               goto out;
>          }
> 
>          if (fs_info->balance_ctl) {
>                  ret = -EINPROGRESS;
> -               goto out_bargs;
> +               goto out;
>          }
> 
>          bctl = kzalloc(sizeof(*bctl), GFP_KERNEL);
>          if (!bctl) {
>                  ret = -ENOMEM;
> -               goto out_bargs;
> +               goto out;
>          }
> 
>          memcpy(&bctl->data, &bargs->data, sizeof(bctl->data));
> @@ -4457,12 +4456,11 @@ static long btrfs_ioctl_balance(struct file 
> *file, void __user *arg)
>          }
> 
>          kfree(bctl);
> -out_bargs:

This looks much better, without the extra label it's easier to read.

But, the @need_unlock variable seems to be uninitialized now, as it's 
only set in case (3), but case (2) and (1) now goes through out which 
needs to check @need_unlock.

Thanks,
Qu

> +out:
>          kfree(bargs);
>          mutex_unlock(&fs_info->balance_mutex);
>          if (need_unlock)
>                  btrfs_exclop_finish(fs_info);
> -out:
>          mnt_drop_write_file(file);
>          return ret;
>   }
> 
> 
> 
>