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Subject: Re: [PATCH] jffs2: move jffs2_init_inode_info() just after allocating
 inode
To:     "zhangyi (F)" <yi.zhang@huawei.com>, <viro@zeniv.linux.org.uk>,
        <linux-mtd@lists.infradead.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Richard Weinberger <richard@nod.at>
CC:     <zhongguohua1@huawei.com>, <daniel@iogearbox.net>,
        <yihuaijie@huawei.com>, <ast@kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
        <chenjie6@huawei.com>
References: <20200106080411.41394-1-yi.zhang@huawei.com>
From:   Hou Tao <houtao1@huawei.com>
Message-ID: <2202d894-5b47-e606-2f58-306ec151626b@huawei.com>
Date:   Thu, 23 Jul 2020 17:58:45 +0800
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Hi,

Cc +Richard +David

On 2020/1/6 16:04, zhangyi (F) wrote:
> After commit 4fdcfab5b553 ("jffs2: fix use-after-free on symlink
> traversal"), it expose a freeing uninitialized memory problem due to
> this commit move the operaion of freeing f->target to
> jffs2_i_callback(), which may not be initialized in some error path of
> allocating jffs2 inode (eg: jffs2_iget()->iget_locked()->
> destroy_inode()->..->jffs2_i_callback()->kfree(f->target)).
> 
Could you please elaborate the scenario in which the use of a uninitialized
f->target is possible ? IMO one case is that there are concurrent
jffs2_lookup() and jffs2 GC on an evicted inode, and two new inodes
are created, and then one needless inode is destroyed.

> Fix this by initialize the jffs2_inode_info just after allocating it.
> 
> Reported-by: Guohua Zhong <zhongguohua1@huawei.com>
> Reported-by: Huaijie Yi <yihuaijie@huawei.com>
> Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
> Cc: stable@vger.kernel.org
> ---
A Fixes tag is also needed here.

>  fs/jffs2/fs.c    | 2 --
>  fs/jffs2/super.c | 2 ++
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/jffs2/fs.c b/fs/jffs2/fs.c
> index ab8cdd9e9325..50a9df7d43a5 100644
> --- a/fs/jffs2/fs.c
> +++ b/fs/jffs2/fs.c
> @@ -270,7 +270,6 @@ struct inode *jffs2_iget(struct super_block *sb, unsigned long ino)
>  	f = JFFS2_INODE_INFO(inode);
>  	c = JFFS2_SB_INFO(inode->i_sb);
>  
> -	jffs2_init_inode_info(f);
>  	mutex_lock(&f->sem);
>  
>  	ret = jffs2_do_read_inode(c, f, inode->i_ino, &latest_node);
> @@ -438,7 +437,6 @@ struct inode *jffs2_new_inode (struct inode *dir_i, umode_t mode, struct jffs2_r
>  		return ERR_PTR(-ENOMEM);
>  
>  	f = JFFS2_INODE_INFO(inode);
> -	jffs2_init_inode_info(f);
>  	mutex_lock(&f->sem);
>  
>  	memset(ri, 0, sizeof(*ri));
> diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
> index 0e6406c4f362..90373898587f 100644
> --- a/fs/jffs2/super.c
> +++ b/fs/jffs2/super.c
> @@ -42,6 +42,8 @@ static struct inode *jffs2_alloc_inode(struct super_block *sb)
>  	f = kmem_cache_alloc(jffs2_inode_cachep, GFP_KERNEL);
>  	if (!f)
>  		return NULL;
> +
> +	jffs2_init_inode_info(f);
>  	return &f->vfs_inode;
>  }
>  
>