linux-kernel - Re: [PATCH v3 3/4] ext4: add EXT4_IGET_BAD flag to prevent unexpected bad inode

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Message-ID: <20221026094147.n3hv6bk6meafc73y@quack3>
Date:   Wed, 26 Oct 2022 11:41:47 +0200
From:   Jan Kara <jack@...e.cz>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yukuai3@...wei.com
Subject: Re: [PATCH v3 3/4] ext4: add EXT4_IGET_BAD flag to prevent
 unexpected bad inode

On Wed 26-10-22 12:23:09, Baokun Li wrote:
> There are many places that will get unhappy (and crash) when ext4_iget()
> returns a bad inode. However, if iget the boot loader inode, allows a bad
> inode to be returned, because the inode may not be initialized. This
> mechanism can be used to bypass some checks and cause panic. To solve this
> problem, we add a special iget flag EXT4_IGET_BAD. Only with this flag
> we'd be returning bad inode from ext4_iget(), otherwise we always return
> the error code if the inode is bad inode.(suggested by Jan Kara)
> 
> Signed-off-by: Baokun Li <libaokun1@...wei.com>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/ext4.h  | 3 ++-
>  fs/ext4/inode.c | 8 +++++++-
>  fs/ext4/ioctl.c | 3 ++-
>  3 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 8d5453852f98..2b574b143bde 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2964,7 +2964,8 @@ int do_journal_get_write_access(handle_t *handle, struct inode *inode,
>  typedef enum {
>  	EXT4_IGET_NORMAL =	0,
>  	EXT4_IGET_SPECIAL =	0x0001, /* OK to iget a system inode */
> -	EXT4_IGET_HANDLE = 	0x0002	/* Inode # is from a handle */
> +	EXT4_IGET_HANDLE = 	0x0002,	/* Inode # is from a handle */
> +	EXT4_IGET_BAD =		0x0004  /* Allow to iget a bad inode */
>  } ext4_iget_flags;
>  
>  extern struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index ae3a836dd9d7..f767340229fd 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5043,8 +5043,14 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
>  	if (IS_CASEFOLDED(inode) && !ext4_has_feature_casefold(inode->i_sb))
>  		ext4_error_inode(inode, function, line, 0,
>  				 "casefold flag without casefold feature");
> -	brelse(iloc.bh);
> +	if (is_bad_inode(inode) && !(flags & EXT4_IGET_BAD)) {
> +		ext4_error_inode(inode, function, line, 0,
> +				 "bad inode without EXT4_IGET_BAD flag");
> +		ret = -EUCLEAN;
> +		goto bad_inode;
> +	}
>  
> +	brelse(iloc.bh);
>  	unlock_new_inode(inode);
>  	return inode;
>  
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index ded535535b27..e0be8026c996 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -375,7 +375,8 @@ static long swap_inode_boot_loader(struct super_block *sb,
>  	blkcnt_t blocks;
>  	unsigned short bytes;
>  
> -	inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO, EXT4_IGET_SPECIAL);
> +	inode_bl = ext4_iget(sb, EXT4_BOOT_LOADER_INO,
> +			EXT4_IGET_SPECIAL | EXT4_IGET_BAD);
>  	if (IS_ERR(inode_bl))
>  		return PTR_ERR(inode_bl);
>  	ei_bl = EXT4_I(inode_bl);
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR