linux-kernel - Re: [PATCH v2] ext4: Make block validity check resistent to sb bh corruption

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Message-ID: <6203563b-ff13-47b2-b630-d710eab47d62@huaweicloud.com>
Date: Fri, 28 Mar 2025 09:52:26 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: Jan Kara <jack@...e.cz>, Baokun Li <libaokun1@...wei.com>,
 Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org,
 linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v2] ext4: Make block validity check resistent to sb bh
 corruption

On 2025/3/28 1:48, Ojaswin Mujoo wrote:
> Block validity checks need to be skipped in case they are called
> for journal blocks since they are part of system's protected
> zone.
> 
> Currently, this is done by checking inode->ino against
> sbi->s_es->s_journal_inum, which is a direct read from the ext4 sb
> buffer head. If someone modifies this underneath us then the
> s_journal_inum field might get corrupted. To prevent against this,
> change the check to directly compare the inode with journal->j_inode.
> 
> **Slight change in behavior**: During journal init path,
> check_block_validity etc might be called for journal inode when
> sbi->s_journal is not set yet. In this case we now proceed with
> ext4_inode_block_valid() instead of returning early. Since systems zones
> have not been set yet, it is okay to proceed so we can perform basic
> checks on the blocks.
> 
> Suggested-by: Baokun Li <libaokun1@...wei.com>
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>

Thanks for the inprovement! Besides the indentation that Jan pointed
out, it looks good to me.

Reviewed-by: Zhang Yi <yi.zhang@...wei.com>

> ---
> 
> ** Changes since v1 [1] **
> 
> - instead of using an sbi field direction check against jorunal->j_inode
> - let block validity perform basic checks on journal blocks as well
> 	during init path
> - kvm-xfstests quick tests are passing
> 
> [1] https://lore.kernel.org/linux-ext4/d1a9328a41029f6210a1924b192a59afcd3c5cee.1741952406.git.ojaswin@linux.ibm.com/
> 
>  fs/ext4/block_validity.c | 5 ++---
>  fs/ext4/inode.c          | 9 +++++----
>  2 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
> index 87ee3a17bd29..e8c5525afc67 100644
> --- a/fs/ext4/block_validity.c
> +++ b/fs/ext4/block_validity.c
> @@ -351,10 +351,9 @@ int ext4_check_blockref(const char *function, unsigned int line,
>  {
>  	__le32 *bref = p;
>  	unsigned int blk;
> +	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
>  
> -	if (ext4_has_feature_journal(inode->i_sb) &&
> -	    (inode->i_ino ==
> -	     le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_journal_inum)))
> +	if (journal && inode == journal->j_inode)
>  		return 0;
>  
>  	while (bref < p+max) {
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 365d31004bd0..8b048be14008 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -384,10 +384,11 @@ static int __check_block_validity(struct inode *inode, const char *func,
>  				unsigned int line,
>  				struct ext4_map_blocks *map)
>  {
> -	if (ext4_has_feature_journal(inode->i_sb) &&
> -	    (inode->i_ino ==
> -	     le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_journal_inum)))
> -		return 0;
> +	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> +
> +	if (journal && inode == journal->j_inode)
> +			return 0;
> +
>  	if (!ext4_inode_block_valid(inode, map->m_pblk, map->m_len)) {
>  		ext4_error_inode(inode, func, line, map->m_pblk,
>  				 "lblock %lu mapped to illegal pblock %llu "