[lvc-project] [PATCH v2] ocfs2: adjust ocfs2_xa_remove_entry() to match UBSAN boundary checks

[Heming Zhao]

On Thu, Dec 11, 2025 at 06:59:49PM +0300, Dmitry Antipov wrote:
> After introducing 2f26f58df041 ("ocfs2: annotate flexible array members
> with __counted_by_le()"), syzbot has reported the following issue:
> 
> UBSAN: array-index-out-of-bounds in fs/ocfs2/xattr.c:1955:3
> index 2 is out of range for type 'struct ocfs2_xattr_entry[]
> __counted_by(xh_count)' (aka 'struct ocfs2_xattr_entry[]')
> ...
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>  ubsan_epilogue+0xa/0x40 lib/ubsan.c:233
>  __ubsan_handle_out_of_bounds+0xe9/0xf0 lib/ubsan.c:455
>  ocfs2_xa_remove_entry+0x36d/0x3e0 fs/ocfs2/xattr.c:1955
>  ...
> 
> To address this issue, 'xh_entries[]' member removal should be performed
> before actually changing 'xh_count', thus making sure that all array
> accesses matches the boundary checks performed by UBSAN.
> 
> Reported-by: syzbot+cf96bc82a588a27346a8 at syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=cf96bc82a588a27346a8
> Signed-off-by: Dmitry Antipov <dmantipov at yandex.ru>

LGTM.
Reviewed-by: Heming Zhao <heming.zhao at suse.com>

> ---
> v2: adjust commit metadata per Heming's notices
> ---
>  fs/ocfs2/xattr.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> index dc1761e84814..de99276d12f0 100644
> --- a/fs/ocfs2/xattr.c
> +++ b/fs/ocfs2/xattr.c
> @@ -1941,8 +1941,7 @@ static void ocfs2_xa_remove_entry(struct ocfs2_xa_loc *loc)
>  	ocfs2_xa_wipe_namevalue(loc);
>  	loc->xl_entry = NULL;
>  
> -	le16_add_cpu(&xh->xh_count, -1);
> -	count = le16_to_cpu(xh->xh_count);
> +	count = le16_to_cpu(xh->xh_count) - 1;
>  
>  	/*
>  	 * Only zero out the entry if there are more remaining.  This is
> @@ -1957,6 +1956,8 @@ static void ocfs2_xa_remove_entry(struct ocfs2_xa_loc *loc)
>  		memset(&xh->xh_entries[count], 0,
>  		       sizeof(struct ocfs2_xattr_entry));
>  	}
> +
> +	xh->xh_count = cpu_to_le16(count);
>  }
>  
>  /*
> -- 
> 2.52.0
>