linux-kernel - Re: [PATCH V3] fs/ntfs3: check if the inode is bad before creating symlink

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Message-ID: <20241121035529.GO3387508@ZenIV>
Date: Thu, 21 Nov 2024 03:55:29 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Lizhi Xu <lizhi.xu@...driver.com>
Cc: almaz.alexandrovich@...agon-software.com, brauner@...nel.org,
	jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, ntfs3@...ts.linux.dev,
	syzbot+73d8fc29ec7cba8286fa@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH V3] fs/ntfs3: check if the inode is bad before creating
 symlink

On Thu, Nov 21, 2024 at 11:13:29AM +0800, Lizhi Xu wrote:
>   user_path_at()->
>     filename_lookup()->
>       path_lookupat()->
>         lookup_last()->
>           walk_component()->
>             __lookup_slow()->
>               ntfs_lookup()->
>                 d_splice_alias()->
> 
> 2. The subsequent chmod fails, causing the inode to be set to bad.

What's wrong with "return an error"?

> 3. During the link operation, d_instantiate() is executed in ntfs_link() to associate the bad inode with the dentry.

Yecchhh...  If nothing else, check for is_bad_inode() should be there
for as long as make_bad_inode() is done on live inodes.