linux-kernel - Re: [PATCH] pipe: fix potential inode leak in create_pipe

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Date:   Wed, 28 Oct 2020 14:00:45 +0800
From:   Zhiqiang Liu <liuzhiqiang26@...wei.com>
To:     Al Viro <viro@...iv.linux.org.uk>
CC:     <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <cai@...hat.com>
Subject: Re: [PATCH] pipe: fix potential inode leak in create_pipe_files()



On 2020/10/28 11:54, Al Viro wrote:
> On Wed, Oct 28, 2020 at 11:03:52AM +0800, Zhiqiang Liu wrote:
>>
>> In create_pipe_files(), if alloc_file_clone() fails, we will call
>> put_pipe_info to release pipe, and call fput() to release f.
>> However, we donot call iput() to free inode.
> 
> Huh?  Have you actually tried to trigger that failure exit?
>
>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>
>> Signed-off-by: Feilong Lin <linfeilong@...wei.com>
>> ---
>>  fs/pipe.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/pipe.c b/fs/pipe.c
>> index 0ac197658a2d..8856607fde65 100644
>> --- a/fs/pipe.c
>> +++ b/fs/pipe.c
>> @@ -924,6 +924,7 @@ int create_pipe_files(struct file **res, int flags)
>>  	if (IS_ERR(res[0])) {
>>  		put_pipe_info(inode, inode->i_pipe);
>>  		fput(f);
>> +		iput(inode);
>>  		return PTR_ERR(res[0]);
> 
> No.  That inode is created with refcount 1.  If alloc_file_pseudo()
> succeeds, the reference we'd been holding has been transferred into
> dentry allocated by alloc_file_pseudo() (and attached to f).
>>>From that point on we do *NOT* own a reference to inode and no
> subsequent failure exits have any business releasing it.
> 
> In particular, alloc_file_clone() DOES NOT create extra references
> to inode, whether it succeeds or fails.  Dropping the reference
> to f will take care of everything.
> 
> If you tried to trigger that failure exit with your patch applied,
> you would've seen double iput(), as soon as you return from sys_pipe()
> to userland and task_work is processed (which is where the real
> destructor of struct file will happen).
> 
> NAK.
> 

Thanks for your patient response. Learned a lot from your reply.
Please ignore the patch.

> .
>