Re: [PATCH v4] ext4: detect invalid INLINE_DATA + EXTENTS flag combination

[Zhang Yi <yi.zhang@huaweicloud.com>]

On 9/30/2025 7:28 PM, Deepanshu Kartikey wrote:
> syzbot reported a BUG_ON in ext4_es_cache_extent() when opening a verity
> file on a corrupted ext4 filesystem mounted without a journal.
> 
> The issue is that the filesystem has an inode with both the INLINE_DATA
> and EXTENTS flags set:
> 
>     EXT4-fs error (device loop0): ext4_cache_extents:545: inode #15:
>     comm syz.0.17: corrupted extent tree: lblk 0 < prev 66
> 
> Investigation revealed that the inode has both flags set:
>     DEBUG: inode 15 - flag=1, i_inline_off=164, has_inline=1, extents_flag=1
> 
> This is an invalid combination since an inode should have either:
> - INLINE_DATA: data stored directly in the inode
> - EXTENTS: data stored in extent-mapped blocks
> 
> Having both flags causes ext4_has_inline_data() to return true, skipping
> extent tree validation in __ext4_iget(). The unvalidated out-of-order
> extents then trigger a BUG_ON in ext4_es_cache_extent() due to integer
> underflow when calculating hole sizes.
> 
> Fix this by detecting this invalid flag combination early in ext4_iget()
> and rejecting the corrupted inode.
> 
> Reported-and-tested-by: syzbot+038b7bf43423e132b308@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=038b7bf43423e132b308
> Suggested-by: Zhang Yi <yi.zhang@huawei.com>
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>

Thanks for the fix, it looks good to me.

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

> 
> ---
> Changes in v4:
> - Move check to right after ext4_set_inode_flags() as suggested by Zhang Yi,
>   since we're checking flags directly (not ext4_has_inline_data() return value)
> 
> Changes in v3:
> - Fix code alignment and use existing function/line variables per Zhang Yi
> 
> Changes in v2:
> - Instead of adding validation in ext4_find_extent(), detect the invalid
>   INLINE_DATA + EXTENTS flag combination in ext4_iget() as suggested by
>   Zhang Yi to avoid redundant checks in the extent lookup path
> ---
>  fs/ext4/inode.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 5b7a15db4953..2fef378dbc97 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5348,6 +5348,14 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
>  	}
>  	ei->i_flags = le32_to_cpu(raw_inode->i_flags);
>  	ext4_set_inode_flags(inode, true);
> +	/* Detect invalid flag combination - can't have both inline data and extents */
> +	if (ext4_test_inode_flag(inode, EXT4_INODE_INLINE_DATA) &&
> +	    ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
> +		ext4_error_inode(inode, function, line, 0,
> +			"inode has both inline data and extents flags");
> +		ret = -EFSCORRUPTED;
> +		goto bad_inode;
> +	}
>  	inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
>  	ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
>  	if (ext4_has_feature_64bit(sb))