Re: [PATCH] loop: Add sanity check for read/write_iter

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2025/4/25 5:40, Lizhi Xu 写道:
> Some file systems do not support read_iter or write_iter, such as selinuxfs
> in this issue.
> So before calling them, first confirm that the interface is supported and
> then call it.
> 
> Reported-by: syzbot+6af973a3b8dfd2faefdc@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=6af973a3b8dfd2faefdc
> Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
> ---
>   drivers/block/loop.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 674527d770dc..4f968e3071ed 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -449,10 +449,15 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
>   	cmd->iocb.ki_flags = IOCB_DIRECT;
>   	cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
>   
> -	if (rw == ITER_SOURCE)
> -		ret = file->f_op->write_iter(&cmd->iocb, &iter);
> -	else
> -		ret = file->f_op->read_iter(&cmd->iocb, &iter);
> +	ret = 0;
> +	if (rw == ITER_SOURCE) {
> +		if (likely(file->f_op->write_iter))
> +			ret = file->f_op->write_iter(&cmd->iocb, &iter);
> +	}
> +	else {
> +		if (likely(file->f_op->read_iter))

"else if" is better?

Zhu Yanjun
> +			ret = file->f_op->read_iter(&cmd->iocb, &iter);
> +	}
>   
>   	lo_rw_aio_do_completion(cmd);
>