linux-kernel - Re: [PATCH v3] ocfs2: validate inline xattr size and entry count in ocfs2_xattr_ibody

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Message-ID: <ef22zw37ifljwla5ifbtrgjrx35gnifqi5lcaxfgabaeydbmco@zbc2eulbbmea>
Date: Wed, 19 Nov 2025 23:36:21 +0800
From: Heming Zhao <heming.zhao@...e.com>
To: Deepanshu Kartikey <kartikey406@...il.com>
Cc: mark@...heh.com, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com, 
	ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	syzbot+ab0ad25088673470d2d9@...kaller.appspotmail.com
Subject: Re: [PATCH v3] ocfs2: validate inline xattr size and entry count in
 ocfs2_xattr_ibody_list

On Mon, Nov 17, 2025 at 05:12:24PM +0530, Deepanshu Kartikey wrote:
> Add comprehensive validation of inline xattr metadata in
> ocfs2_xattr_ibody_list() to prevent out-of-bounds access and
> use-after-free bugs when processing corrupted inline xattrs.
> 
> The patch adds two critical validations:
> 
> 1. Validates i_xattr_inline_size before use:
>    - Ensures it does not exceed block size
>    - Ensures it is at least large enough for xattr header
>    - Prevents pointer arithmetic with corrupted size values that could
>      point outside the inode block
> 
> 2. Validates xattr entry count (xh_count):
>    - Calculates maximum entries that can fit in the inline space
>    - Rejects counts that exceed this limit
>    - Prevents out-of-bounds array access in subsequent code
> 
> Without these checks, a corrupted filesystem with invalid inline xattr
> metadata can cause the code to access memory beyond the allocated space.
> For example:
> - A corrupted i_xattr_inline_size of 0 would cause header pointer
>   calculation to point past the end of the block
> - A corrupted xh_count of 20041 with inline_size of 256 would cause
>   array access beyond the 7 entries that actually fit, leading to
>   use-after-free when accessing freed memory pages

The following patch code is LGTM, but I can't understand the meaning of above
xh_cont:20041. Please show more details for the value 20041.

In my view,
the sizeof(struct ocfs2_xattr_header) is 16 (by: 2+2+2+2+(4+2+2)+0)
the sizeof(struct ocfs2_xattr_entry) is 16 (by: 4+2+1+1+8).
when the inline_size is 256.
the max number of entries for inline mode: (256-16) / 16 = 15.
therefore, the xh_count of 22 (by: 15+7) corresponds to a value that is 7
entries beyond the boundary.

Thanks,
Heming
> 
> The validation uses the correct inline_size (from di->i_xattr_inline_size)
> rather than block size, ensuring accurate bounds checking for inline
> xattrs specifically.
> 
> Reported-by: syzbot+ab0ad25088673470d2d9@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=ab0ad25088673470d2d9
> Tested-by: syzbot+ab0ad25088673470d2d9@...kaller.appspotmail.com
> Suggested-by: Heming Zhao <heming.zhao@...e.com>
> Link: https://lore.kernel.org/all/20251111073831.2027072-1-kartikey406@gmail.com/ [v1]
> Link: https://lore.kernel.org/all/20251117063217.5690-1-kartikey406@gmail.com/T/ [v2]
> Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
> ---
> Changes in v3:
>  - Moved validation from ocfs2_xattr_list_entries() to
>    ocfs2_xattr_ibody_list() to use correct inline size calculation
>    (suggested by Heming Zhao)
>  - Added validation of i_xattr_inline_size before use
>  - Added validation of xattr entry count against inline space
>  - Changed return value to -EFSCORRUPTED for consistency
> ---
>  fs/ocfs2/xattr.c | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> index d70a20d29e3e..98fd4f3f2d2d 100644
> --- a/fs/ocfs2/xattr.c
> +++ b/fs/ocfs2/xattr.c
> @@ -971,13 +971,39 @@ static int ocfs2_xattr_ibody_list(struct inode *inode,
>  	struct ocfs2_xattr_header *header = NULL;
>  	struct ocfs2_inode_info *oi = OCFS2_I(inode);
>  	int ret = 0;
> +	u16 xattr_count;
> +	size_t max_entries;
> +	u16 inline_size;
>  
>  	if (!(oi->ip_dyn_features & OCFS2_INLINE_XATTR_FL))
>  		return ret;
>  
> +	inline_size = le16_to_cpu(di->i_xattr_inline_size);
> +
> +	/* Validate inline size is reasonable */
> +	if (inline_size > inode->i_sb->s_blocksize ||
> +	    inline_size < sizeof(struct ocfs2_xattr_header)) {
> +		ocfs2_error(inode->i_sb,
> +			    "Invalid xattr inline size %u in inode %llu\n",
> +			    inline_size,
> +			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
> +		return -EFSCORRUPTED;
> +	}
> +
>  	header = (struct ocfs2_xattr_header *)
> -		 ((void *)di + inode->i_sb->s_blocksize -
> -		 le16_to_cpu(di->i_xattr_inline_size));
> +		 ((void *)di + inode->i_sb->s_blocksize - inline_size);
> +
> +	xattr_count = le16_to_cpu(header->xh_count);
> +	max_entries = (inline_size - sizeof(struct ocfs2_xattr_header)) /
> +		       sizeof(struct ocfs2_xattr_entry);
> +
> +	if (xattr_count > max_entries) {
> +		ocfs2_error(inode->i_sb,
> +			    "xattr entry count %u exceeds maximum %zu in inode %llu\n",
> +			    xattr_count, max_entries,
> +			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
> +		return -EFSCORRUPTED;
> +	}
>  
>  	ret = ocfs2_xattr_list_entries(inode, header, buffer, buffer_size);
>  
> -- 
> 2.43.0
>