[PATCH] pipe: fix potential inode leak in create_pipe_files()

[PATCH] pipe: fix potential inode leak in create_pipe_files()

[Zhiqiang Liu]

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.

Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Feilong Lin <linfeilong@huawei.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]);
 	}
 	res[0]->private_data = inode->i_pipe;
-- 
2.19.1

Re: [PATCH] pipe: fix potential inode leak in create_pipe_files()

[Al Viro]

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@huawei.com>
> Signed-off-by: Feilong Lin <linfeilong@huawei.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.

Re: [PATCH] pipe: fix potential inode leak in create_pipe_files()

[Zhiqiang Liu]

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@huawei.com>
>> Signed-off-by: Feilong Lin <linfeilong@huawei.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.

> .
>