Re: [PATCH 1/3] io_uring: don't use req->work.creds for inline requests

[Pavel Begunkov <asml.silence@gmail.com>]

On 26/05/2020 09:43, Xiaoguang Wang wrote:
> In io_init_req(), if uers requires a new credentials, currently we'll
> save it in req->work.creds, but indeed io_wq_work is designed to describe
> needed running environment for requests that will go to io-wq, if one
> request is going to be submitted inline, we'd better not touch io_wq_work.
> Here add a new 'const struct cred *creds' in io_kiocb, if uers requires a
> new credentials, inline requests can use it.
> 
> This patch is also a preparation for later patch.

What's the difference from keeping only one creds field in io_kiocb (i.e.
req->work.creds), but handling it specially (i.e. always initialising)? It will
be a lot easier than tossing it around.

Also, the patch doubles {get,put}_creds() for sqe->personality case, and that's
extra atomics without a good reason.

> 
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
> ---
>  fs/io_uring.c | 23 +++++++++++++++--------
>  1 file changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 2af87f73848e..788d960abc69 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -635,6 +635,7 @@ struct io_kiocb {
>  	unsigned int		flags;
>  	refcount_t		refs;
>  	struct task_struct	*task;
> +	const struct cred	*creds;
>  	unsigned long		fsize;
>  	u64			user_data;
>  	u32			result;
> @@ -1035,8 +1036,10 @@ static inline void io_req_work_grab_env(struct io_kiocb *req,
>  		mmgrab(current->mm);
>  		req->work.mm = current->mm;
>  	}
> -	if (!req->work.creds)
> +	if (!req->creds)
>  		req->work.creds = get_current_cred();
> +	else
> +		req->work.creds = get_cred(req->creds);
>  	if (!req->work.fs && def->needs_fs) {
>  		spin_lock(&current->fs->lock);
>  		if (!current->fs->in_exec) {
> @@ -1368,6 +1371,9 @@ static void __io_req_aux_free(struct io_kiocb *req)
>  	if (req->flags & REQ_F_NEED_CLEANUP)
>  		io_cleanup_req(req);
>  
> +	if (req->creds)
> +		put_cred(req->creds);
> +
>  	kfree(req->io);
>  	if (req->file)
>  		io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE));
> @@ -5673,13 +5679,13 @@ static void __io_queue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  again:
>  	linked_timeout = io_prep_linked_timeout(req);
>  
> -	if (req->work.creds && req->work.creds != current_cred()) {
> +	if (req->creds && req->creds != current_cred()) {
>  		if (old_creds)
>  			revert_creds(old_creds);
> -		if (old_creds == req->work.creds)
> +		if (old_creds == req->creds)
>  			old_creds = NULL; /* restored original creds */
>  		else
> -			old_creds = override_creds(req->work.creds);
> +			old_creds = override_creds(req->creds);
>  	}
>  
>  	ret = io_issue_sqe(req, sqe, true);
> @@ -5970,11 +5976,12 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
>  
>  	id = READ_ONCE(sqe->personality);
>  	if (id) {
> -		req->work.creds = idr_find(&ctx->personality_idr, id);
> -		if (unlikely(!req->work.creds))
> +		req->creds = idr_find(&ctx->personality_idr, id);
> +		if (unlikely(!req->creds))
>  			return -EINVAL;
> -		get_cred(req->work.creds);
> -	}
> +		get_cred(req->creds);
> +	} else
> +		req->creds = NULL;
>  
>  	/* same numerical values with corresponding REQ_F_*, safe to copy */
>  	req->flags |= sqe_flags;
> 

-- 
Pavel Begunkov