linux-kernel - Re: 回复: [PATCH V5] loop: Add sanity check for read/write

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Message-ID: <aCwlRMEuvvP31UGG@infradead.org>
Date: Mon, 19 May 2025 23:46:28 -0700
From: "hch@...radead.org" <hch@...radead.org>
To: "Xu, Lizhi" <Lizhi.Xu@...driver.com>
Cc: Christian Hesse <mail@...rm.de>, "axboe@...nel.dk" <axboe@...nel.dk>,
	"christian@...sel.eu" <christian@...sel.eu>,
	"hch@...radead.org" <hch@...radead.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ming.lei@...hat.com" <ming.lei@...hat.com>,
	"syzbot+6af973a3b8dfd2faefdc@...kaller.appspotmail.com" <syzbot+6af973a3b8dfd2faefdc@...kaller.appspotmail.com>,
	"syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>
Subject: Re: 回复: [PATCH V5] loop: Add sanity
 check for read/write_iter

On Tue, May 20, 2025 at 06:29:48AM +0000, Xu, Lizhi wrote:
> I figured out your steps to reproduce, and yes, this problem will occur if you do losetup with a file in a filesystem that does not support read_iter, which is what this patch does.

isofs does support read_iter, without that it would not have worked
before either. That is not the problem.  It must be related to
the FMODE_WRITE check - i.e. we have a writable FD here, but a file
system that does not actually supports writes.  Which honestly feels
weird, but we'll have to figure it out to unbreak these setups.