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

[Baokun Li]

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@xxxxxxxxxx>
> Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
Thanks for the patch！Looks good to me, except for the extra indentation
pointed out by Honza. With that fixed feel free to add:

Reviewed-by: Baokun Li <libaokun1@xxxxxxxxxx>


Cheers,
Baokun
> ---
>
> ** 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@xxxxxxxxxxxxx/
>
>   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 "