linux-ext4 - Re: [PATCH] ext4: fix WARNING in lock_two

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Date: Mon, 25 Dec 2023 09:38:51 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Edward Adam Davis <eadavis@...com>,
	<syzbot+2c4a3b922a860084cc7f@...kaller.appspotmail.com>
CC: <adilger.kernel@...ger.ca>, <linux-ext4@...r.kernel.org>,
	<linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<syzkaller-bugs@...glegroups.com>, <tytso@....edu>, yangerkun
	<yangerkun@...wei.com>, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH] ext4: fix WARNING in lock_two_nondirectories

On 2023/12/24 19:53, Edward Adam Davis wrote:
> If inode is the ext4 boot loader inode, then when it is a directory, the inode
> should also be set to bad inode.
>
> Reported-and-tested-by: syzbot+2c4a3b922a860084cc7f@...kaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@...com>
> ---
>   fs/ext4/inode.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 61277f7f8722..b311f610f008 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4944,8 +4944,12 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
>   		inode->i_fop = &ext4_file_operations;
>   		ext4_set_aops(inode);
>   	} else if (S_ISDIR(inode->i_mode)) {
> -		inode->i_op = &ext4_dir_inode_operations;
> -		inode->i_fop = &ext4_dir_operations;
> +		if (ino == EXT4_BOOT_LOADER_INO)
> +			make_bad_inode(inode);
Marking the boot loader inode as a bad inode here is useless,
EXT4_IGET_BAD allows us to get a bad boot loader inode.
In my opinion, it doesn't make sense to call lock_two_nondirectories()
here to determine if the inode is a regular file or not, since the logic
for dealing with non-regular files comes after the locking, so calling
lock_two_inodes() directly here will suffice.

Merry Christmas!
Baokun
> +		else {
> +			inode->i_op = &ext4_dir_inode_operations;
> +			inode->i_fop = &ext4_dir_operations;
> +		}
>   	} else if (S_ISLNK(inode->i_mode)) {
>   		/* VFS does not allow setting these so must be corruption */
>   		if (IS_APPEND(inode) || IS_IMMUTABLE(inode)) {