Re: [PATCH v2 06/14] vfs: add some allowed open flags to vfs_lookup_open()

[Jori Koolstra <jkoolstra@xs4all.nl>]

> Op 19-09-2026 04:06 CEST schreef NeilBrown <neilb@ownmail.net>:
> 
>  
> From: NeilBrown <neil@brown.name>
> 
> vfs_lookup_open() must allow:
>   O_LARGEFILE so that large files can be opened.
>   O_NONBLOCK so that break_lease() can be asked to return -EWOULDBLOCK.
> 
> Also O_NOFOLLOW as we don't/can't handle symlinks.  In fact we
> should enforce O_NOFOLLOW for the same reason we enforce __O_REGULAR.

I don't know all the NFS background, but: you can handle intermediate symlinks
but not trailing ones? Why is that?

> 
> Signed-off-by: NeilBrown <neil@brown.name>
> ---
>  fs/namei.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 0f69abb3743b..a08f37aca3e1 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4632,11 +4632,12 @@ struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
>  	int error = 0;
>  
>  	WARN_ONCE(mode & ~S_IALLUGO, "mode must only have permission bits");
> -	WARN_ONCE(open_flag & ~(O_ACCMODE|O_CREAT|O_EXCL|O_TRUNC|__O_REGULAR),
> +	WARN_ONCE(open_flag & ~(O_ACCMODE|O_CREAT|O_EXCL|O_TRUNC|__O_REGULAR|
> +				O_NONBLOCK|O_LARGEFILE|O_NOFOLLOW),
>  		  "open_flag has unsupported flags");
>  
>  	mode |= S_IFREG;
> -	open_flag |= __O_REGULAR;
> +	open_flag |= __O_REGULAR | O_NOFOLLOW;

What does __O_REGULAR | O_NOFOLLOW do? Does __O_REGULAR only block opening
if the final resolved thing is not a regular file, or does is also block
trailing symlinks? Afaict, the former.

>  
>  	error = lookup_noperm_common(last, parent->dentry);
>  	if (error)
> -- 
> 2.50.0.107.gf914562f5916.dirty