2020-10-29 00:36:44

by Zhiqiang Liu

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

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 <[email protected]>
Signed-off-by: Feilong Lin <[email protected]>
---
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

2020-10-29 09:01:55

by Al Viro

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

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 <[email protected]>
> Signed-off-by: Feilong Lin <[email protected]>
> ---
> 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.