From: Al Viro <viro@zeniv.linux.org.uk>
To: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Cc: linux-fsdevel@vger.kernel.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
cai@redhat.com
Subject: Re: [PATCH] pipe: fix potential inode leak in create_pipe_files()
Date: Wed, 28 Oct 2020 03:54:53 +0000 [thread overview]
Message-ID: <20201028035453.GI3576660@ZenIV.linux.org.uk> (raw)
In-Reply-To: <779f767d-c08b-0c03-198e-06270100d529@huawei.com>
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.
next prev parent reply other threads:[~2020-10-29 7:34 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 3:03 [PATCH] pipe: fix potential inode leak in create_pipe_files() Zhiqiang Liu
2020-10-28 3:54 ` Al Viro [this message]
2020-10-28 6:00 ` Zhiqiang Liu
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