linux-kernel - Re: [PATCH v3] ext4: detect invalid INLINE

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Message-ID: <989a25da-c1a2-4541-a1a9-42b357276437@huaweicloud.com>
Date: Tue, 30 Sep 2025 19:08:16 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: Deepanshu Kartikey <kartikey406@...il.com>
Cc: tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 syzbot+038b7bf43423e132b308@...kaller.appspotmail.com,
 Zhang Yi <yi.zhang@...wei.com>
Subject: Re: [PATCH v3] ext4: detect invalid INLINE_DATA + EXTENTS flag
 combination

On 9/30/2025 6:25 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@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=038b7bf43423e132b308
> Suggested-by: Zhang Yi <yi.zhang@...wei.com>
> Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>

Thanks for the patch! It looks good to me.

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

> ---
> Changes in v3:
> - Fix code alignment and use existing function/line variables per Zhang Yi
> - Keep check after ret = 0 where all inode fields are initialized, as
>   i_inline_off gets set during inode initialization after ext4_set_inode_flags()
> 
> 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 | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 5b7a15db4953..5c97de5775c7 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5445,6 +5445,15 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
>  	}
>  
>  	ret = 0;
> +	/* 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;
> +	}
> +
>  	if (ei->i_file_acl &&
>  	    !ext4_inode_block_valid(inode, ei->i_file_acl, 1)) {
>  		ext4_error_inode(inode, function, line, 0,