linux-kernel - Re: [PATCH] shmem: fix __shmem_file

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Date:   Tue, 28 Mar 2017 11:54:33 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Vito Caputo'" <vcaputo@...garu.com>, <hughd@...gle.com>
Cc:     "'linux-kernel'" <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [PATCH] shmem: fix __shmem_file_setup error path leaks


On March 28, 2017 1:06 AM Vito Caputo wrote:
> 
> The existing path and memory cleanups appear to be in reverse order, and
> there's no iput() potentially leaking the inode in the last two error gotos.
> 
> Also make put_memory shmem_unacct_size() conditional on !inode since if we
> entered cleanup at put_inode, shmem_evict_inode() occurs via
> iput()->iput_final(), which performs the shmem_unacct_size() for us.
> 
> Signed-off-by: Vito Caputo <vcaputo@...garu.com>
> ---
> 
> This caught my eye while looking through the memfd_create() implementation.
> Included patch was compile tested only...
> 
>  mm/shmem.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index e67d6ba..a1a84eaf 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -4134,7 +4134,7 @@ static struct file *__shmem_file_setup(const char *name, loff_t size,
>  				       unsigned long flags, unsigned int i_flags)
>  {
>  	struct file *res;
> -	struct inode *inode;
> +	struct inode *inode = NULL;
>  	struct path path;
>  	struct super_block *sb;
>  	struct qstr this;
> @@ -4162,7 +4162,7 @@ static struct file *__shmem_file_setup(const char *name, loff_t size,
>  	res = ERR_PTR(-ENOSPC);
>  	inode = shmem_get_inode(sb, NULL, S_IFREG | S_IRWXUGO, 0, flags);
>  	if (!inode)
> -		goto put_memory;
> +		goto put_path;
> 
>  	inode->i_flags |= i_flags;
>  	d_instantiate(path.dentry, inode);

After this routine, the inode is in use of the dcache, as its comment says.

> @@ -4170,19 +4170,22 @@ static struct file *__shmem_file_setup(const char *name, loff_t size,
>  	clear_nlink(inode);	/* It is unlinked */
>  	res = ERR_PTR(ramfs_nommu_expand_for_mapping(inode, size));
>  	if (IS_ERR(res))
> -		goto put_path;
> +		goto put_inode;
> 
>  	res = alloc_file(&path, FMODE_WRITE | FMODE_READ,
>  		  &shmem_file_operations);
>  	if (IS_ERR(res))
> -		goto put_path;
> +		goto put_inode;
> 
>  	return res;
> 
> -put_memory:
> -	shmem_unacct_size(flags, size);
> +put_inode:
> +	iput(inode);
>  put_path:
>  	path_put(&path);
> +put_memory:
> +	if (!inode)
> +		shmem_unacct_size(flags, size);
>  	return res;
>  }
> 
> --
> 2.1.4