[PATCH] net/9p: fix potential refcnt problem of trans module

[PATCH] net/9p: fix potential refcnt problem of trans module

[Chengguang Xu]

When specifying trans_mod multiple times in a mount,
it may cause inaccurate refcount of trans module. Also,
in the error case of option parsing, we should put the
trans module if we have already got.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
---
 net/9p/client.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index b433aff..7ccfb4b 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -190,7 +190,9 @@ static int parse_opts(char *opts, struct p9_client *clnt)
 				p9_debug(P9_DEBUG_ERROR,
 					 "problem allocating copy of trans arg\n");
 				goto free_and_return;
-			 }
+			}
+
+			v9fs_put_trans(clnt->trans_mod);
 			clnt->trans_mod = v9fs_get_trans_by_name(s);
 			if (clnt->trans_mod == NULL) {
 				pr_info("Could not find request transport: %s\n",
@@ -226,6 +228,7 @@ static int parse_opts(char *opts, struct p9_client *clnt)
 	}
 
 free_and_return:
+	v9fs_put_trans(clnt->trans_mod);
 	kfree(tmp_options);
 	return ret;
 }
-- 
1.8.3.1

Re: [V9fs-developer] [PATCH] net/9p: fix potential refcnt problem of trans module

[jiangyiwen]

On 2018/3/27 20:49, Chengguang Xu wrote:
> When specifying trans_mod multiple times in a mount,
> it may cause inaccurate refcount of trans module. Also,
> in the error case of option parsing, we should put the
> trans module if we have already got.
> 
> Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
> ---
>  net/9p/client.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/9p/client.c b/net/9p/client.c
> index b433aff..7ccfb4b 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -190,7 +190,9 @@ static int parse_opts(char *opts, struct p9_client *clnt)
>  				p9_debug(P9_DEBUG_ERROR,
>  					 "problem allocating copy of trans arg\n");
>  				goto free_and_return;
> -			 }
> +			}
> +
> +			v9fs_put_trans(clnt->trans_mod);

I think this should return error if using multiple times
in a mount.

>  			clnt->trans_mod = v9fs_get_trans_by_name(s);
>  			if (clnt->trans_mod == NULL) {
>  				pr_info("Could not find request transport: %s\n",
> @@ -226,6 +228,7 @@ static int parse_opts(char *opts, struct p9_client *clnt)
>  	}
>  
>  free_and_return:
> +	v9fs_put_trans(clnt->trans_mod);

This looks good.

>  	kfree(tmp_options);
>  	return ret;
>  }
> 

Re: [V9fs-developer] [PATCH] net/9p: fix potential refcnt problem of trans module

[cgxu519]

在 2018年3月28日，上午10:10，jiangyiwen <jiangyiwen@huawei.com> 写道：
> 
> On 2018/3/27 20:49, Chengguang Xu wrote:
>> When specifying trans_mod multiple times in a mount,
>> it may cause inaccurate refcount of trans module. Also,
>> in the error case of option parsing, we should put the
>> trans module if we have already got.
>> 
>> Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
>> ---
>> net/9p/client.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/net/9p/client.c b/net/9p/client.c
>> index b433aff..7ccfb4b 100644
>> --- a/net/9p/client.c
>> +++ b/net/9p/client.c
>> @@ -190,7 +190,9 @@ static int parse_opts(char *opts, struct p9_client *clnt)
>> 				p9_debug(P9_DEBUG_ERROR,
>> 					 "problem allocating copy of trans arg\n");
>> 				goto free_and_return;
>> -			 }
>> +			}
>> +
>> +			v9fs_put_trans(clnt->trans_mod);
> 
> I think this should return error if using multiple times
> in a mount.

Fail or retake are just different policies how to deal with this kind of situation,
most filesystems in kernel choose retaking new value, so we’d better keep consistence
with others unless there is a necessary reason.

Thanks,
Chengguang.


> 
>> 			clnt->trans_mod = v9fs_get_trans_by_name(s);
>> 			if (clnt->trans_mod == NULL) {
>> 				pr_info("Could not find request transport: %s\n",
>> @@ -226,6 +228,7 @@ static int parse_opts(char *opts, struct p9_client *clnt)
>> 	}
>> 
>> free_and_return:
>> +	v9fs_put_trans(clnt->trans_mod);
> 
> This looks good.
> 
>> 	kfree(tmp_options);
>> 	return ret;
>> }
>> 
> 
> 

Re: [V9fs-developer] [PATCH] net/9p: fix potential refcnt problem of trans module

[jiangyiwen]

On 2018/3/28 10:52, cgxu519@gmx.com wrote:
> 在 2018年3月28日，上午10:10，jiangyiwen <jiangyiwen@huawei.com> 写道：
>>
>> On 2018/3/27 20:49, Chengguang Xu wrote:
>>> When specifying trans_mod multiple times in a mount,
>>> it may cause inaccurate refcount of trans module. Also,
>>> in the error case of option parsing, we should put the
>>> trans module if we have already got.
>>>
>>> Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
>>> ---
>>> net/9p/client.c | 5 ++++-
>>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/net/9p/client.c b/net/9p/client.c
>>> index b433aff..7ccfb4b 100644
>>> --- a/net/9p/client.c
>>> +++ b/net/9p/client.c
>>> @@ -190,7 +190,9 @@ static int parse_opts(char *opts, struct p9_client *clnt)
>>> 				p9_debug(P9_DEBUG_ERROR,
>>> 					 "problem allocating copy of trans arg\n");
>>> 				goto free_and_return;
>>> -			 }
>>> +			}
>>> +
>>> +			v9fs_put_trans(clnt->trans_mod);
>>
>> I think this should return error if using multiple times
>> in a mount.
> 
> Fail or retake are just different policies how to deal with this kind of situation,
> most filesystems in kernel choose retaking new value, so we’d better keep consistence
> with others unless there is a necessary reason.
> 
> Thanks,
> Chengguang.
> 

Yes, you're right, most filesystems retake indeed the new value.

Reviewed-by: Yiwen Jiang <jiangyiwen@huawei.com>

> 
>>
>>> 			clnt->trans_mod = v9fs_get_trans_by_name(s);
>>> 			if (clnt->trans_mod == NULL) {
>>> 				pr_info("Could not find request transport: %s\n",
>>> @@ -226,6 +228,7 @@ static int parse_opts(char *opts, struct p9_client *clnt)
>>> 	}
>>>
>>> free_and_return:
>>> +	v9fs_put_trans(clnt->trans_mod);
>>
>> This looks good.
>>
>>> 	kfree(tmp_options);
>>> 	return ret;
>>> }
>>>
>>
>>
> 
> 
> .
>